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• Decadal changes in soil water-holding capacity were assessed using field surveys. • Soil erosion and climate change decreased soil water-holding capacity. • The decline in soil water-holding capacity could exacerbate vegetation degradation. Environmental changes on the Tibetan Plateau could affect not only the livelihoods of local people but also the food and environmental security of downstream people. Soil water-holding capacity (WHC) governs soil functioning in ecosystems, could be significantly altered by the accelerated climate change and vegetation degradation experienced by the Tibetan Plateau's alpine ecosystem. However, it remains unclear regarding the direction and magnitude of this feedback. Here, we assessed the responses of WHC to the combined impacts of climate change and vegetation degradation across the Tibetan Plateau over the past decades based on a regional resampling campaign, including 148 well-matched sampling sites, conducted in the 1980s and 2020. We observed an overall decrease in the WHC in the study area in response to a warmer climate and increased soil erosion. The decrease in the topsoil (notably 0–20 cm) was more significant than that in the subsoil (notably 20–50 cm). Average soil available water content (AWC) decreased from 0.13 to 0.10 cm3 cm−3 (p < 0.0001) for topsoil, and from 0.10 to 0.09 cm3 cm−3 (p < 0.01) for subsoil. The changes in AWC were primarily explained by soil erosion (11.3 %) and climate change (9.2 %). Furthermore, the decline in AWC results in a significant decrease in soil productivity, which may exacerbate vegetation degradation and increase the susceptibility of alpine ecosystems to disturbances. These findings suggest that soil erosion control is still an urgent task for environmental protection on the Tibetan Plateau and that increasing WHC is an important goal of adaptation measures. [ABSTRACT FROM AUTHOR]

[Display omitted] • Soil inorganic N pools are higher in fixed dune than in dune grassland. • Soil NO 3 −-N concentration increase with decrease in precipitation. • Altered precipitation patterns do not change soil N transformation. • Soil N transformation increases with EC, NO 3 −-N and NH 4 +-N concentrations. The soil nitrogen (N) cycle and transformation rate are susceptible to precipitation regime changes in semiarid sandy ecosystems, and they play important roles in both the soil fertility and in plant interactions. However, the response mechanisms of soil N transformation to changing precipitation regimes in semiarid ecosystems are still unclear. Thus, we conducted a three-year rainfall manipulation experiment along a landscape evolution gradient from fixed dunes to dune grasslands in a semiarid sandy region of northern China during the growing season (from May to September) between 2017 and 2019. The study included a contrast (P0: natural precipitation) and four treatments in which precipitation was decreased and increased by 60 % [P(− S) and P(+ S)] between May and September and decreased and increased by 100 % [(P(− J) and P(+ J)] between May and June. The soil nitrate nitrogen (NO 3 −-N) and inorganic N concentrations significantly increased under P(− S) and P(− J) (P < 0.05) in both fixed dunes and dune grasslands during the growing season. P(− S) and P(− J) significantly increased the soil net nitrification rate (R n) and net N mineralization rate (R m) only in July, with R m significantly increasing with sampling months and years (P < 0.001). The structural equation model showed that R n and R m did not change with water availability variation, and an increase in R m caused by the direct effects of increased precipitation was offset by its indirect effects mediated by reducing electrical conductivity and soil NO 3 −-N concentration while increasing soil water content and vegetation cover. Soil properties and vegetation characteristics were the main factors affecting soil N transformation during the growing season. Our findings are vital for understanding the seasonal patterns, cumulative N transformation, and possible climate change feedback of semiarid sandy land. [ABSTRACT FROM AUTHOR]

[Display omitted] • Salinity varied with time, space, topography and land use activities. • Salinity decreased with increasing distance from the coastline of the Bay of Bengal. • Polder restricts direct salinization of coastal soils. • Landsat imagery based salinity indexes can reliably predict soil salinity. • A large coastal area turned into saline in the last few decades. Salinity in soils and water of coastal tracts in Bangladesh, one of the major challenges for agriculture, varies significantly due to multiple stressors, including the consequences of rapid changes in the climate pattern. However, their dynamics has not been studied in detail accentuating its importance for the management of agriculture. Here, we examined such changes along zones - defined by spatial proximity from the seafront towards inland in the south-central coast of Bangladesh. Samples of soil and water were collected at single-month intervals between November 2020 and June 2021. In April, a comprehensive soil sampling was conducted to examine spatial variability in relation to soil type and land use. Moreover, Landsat imagery-based salinity index was calculated. Our results showed that soil and water salinity gradually increased from January onwards and peaked during May. It decreased gradually from the seafront to inland, suggesting direct and indirect intrusion of salinity from the sea. A significant non-linear relationship was found between Landsat imagery-based salinity index and measures values (r2 = 0.79, p < 0.01), indicating the Landsat imagery- based estimate could potentially be used for agriculture. Our observation also showed that salinity to soil and water was significantly low in highlands, croplands, and interior of polders as compared respectively to that of low land, fallow land, and exterior of polders. Our estimation of salinity in soil and water of the south-central coast of Bangladesh was significantly higher than that of historical records. This study, thus, would contribute to contemporary policy issues on cropland management along coastal Bangladesh. [ABSTRACT FROM AUTHOR]

• Leaf and soil ecological stoichiometry vary with environmental conditions. • Depressions soil exhibited the highest C, N, and P contents and C:P and N:P ratios. • Leaf stoichiometric characteristics were positively correlated with soil moisture. • Plant community differences resulted from soil hydrological condition variations. • Soil water content was the main factor affecting leaf C, N, and P stoichiometry. Ecological stoichiometry, a novel method for predicting nutrient cycling rates in different habitats, represents the demands of an organism for natural resources and links different levels of biogeochemical cycling. In this study, plant and soil carbon (C), nitrogen (N), and phosphorus (P) concentrations, their stoichiometric characteristics (C:N, C:P, and N:P ratios), and other physicochemical properties of soil were characterized using 243 soil and 81 plant samples collected from three habitats—hummocks, depressions, and meadows—in the marshy wetlands of West China. The results showed that leaf N and P concentrations, soil C, N, and P storage and concentrations, and C:N, C:P, and N:P ratios differed significantly among the three habitats (p < 0.05). Kobresia humilis leaves had the highest N and P content, followed by the leaves of Kobresia tibetica , while Carex mullis leaves had the lowest N and P content. The surface soil of depressions exhibited the highest C, N, C:P, and N:P ratios, hummocks exhibited the highest C:N ratio, whereas meadows exhibited the lowest C and N contents and C:N, and C:P ratios. A structural equation model (SEM) verified that leaf C, N, and P contents and C:P and N:P ratios were positively correlated with soil moisture (SM) and soil organic C contents, whereas the leaf C:N ratio was significantly and negatively correlated with SM content and bulk density. Our findings highlight the ability of alpine marshy wetlands to maintain and even increase the current C, N, and P storage capacities of the ecosystem under increased flooding in the study area. [ABSTRACT FROM AUTHOR]

[Display omitted] • Fire is increasing in zone of patchy Xing'an permafrost protected by ecosystems. • Forest fire has evident influences on boreal ecosystem composition and nutrients. • Forest fire induced expansion of graminoids and tall shrubs in shrub wetlands. • Fires resulted in a massive loss of soil total carbon and nitrogen storages. • Changes in ground temperature and active layer thickness are evident after fires. In boreal regions, wildfires have a major impact on vegetation and permafrost. The ecosystem-protected Xing'an permafrost is sensitive to warming climate and wildfires, particularly on the southern margin of boreal coniferous forest and patchy permafrost zone. However, it remains unclear how fire disturbances are linked with changes in ecosystem composition and soil nutrients in the permafrost zones of Northeast China. Here, 13 years after the fire in the Yile'huli mountain knots, we investigated the parameters like vegetation cover, ground temperatures, active layer thickness, and soil carbon and nitrogen storage at burned and unburned sites of shrub wetlands. The fire resulted in ground warming of 0.1–5.0 °C at depths of 1.0–20.0 m and active layer deepening of 0.5 m, and gravimetric soil moisture content increasing of 26%-266%. Fire also increased the number of herbs and tall shrubs. After the fire, graminoids and tall shrubs increased significantly, and the species of herbs increased by five species. However, dwarf shrubs like Ledum palustre and Vaccinium uliginosum were missing from the burned site. A massive loss of total organic carbon (TOC) (248.40 t C/hm2) and nitrogen (TN) (11.87 t N/hm2) was observed by comparing their storage at burned and unburned sites. These results highlighted that the post-fire responses of vegetation cover and TOC and TN storage were dependent on the thermal regimes of near-surface permafrost and active layer, recovery of vegetation and organic layer, and soil moisture content. This study can provide an important reference for carbon storage and emission in boreal shrub wetlands under a warming climate and increasing fire disturbances. [ABSTRACT FROM AUTHOR]

[Display omitted] • Peeling soil in layers can simulate progressive thawing and detachment. • Outermost layers thawed first and were water saturated with the lowest EC. • Inner core thawed last and was driest with the greatest EC. • Progressively thawed layers differed in microbial properties and CO 2 emission rates. Freeze–thaw events can profoundly reorganise water, salts, and nutrients within the soil matrix, which consequently disturbs soil microbes and perturbs carbon metabolism. However, it remains unclear how soil microbial properties differentiate as they progressively thaw and detach from the still frozen layer as often occurs in a sloped field. In this study, a Mollisol (< 0.5 mm) was refilled into columns and frozen at −15 °C for 12 h. To simulate detachment while thawing, the frozen soil columns were progressively peeled off, from the outer to the inner core, into six layers (T1 ∼ T6). Our results show that: (1) The soil water content significantly declined from 95.3% in the outermost layer T1 to the inner core T6 of 24.7%, whilst the soil electrical conductivity evidently increased from 45.8 μS·cm−1 in the T1 to 73.7 μS·cm−1 in the T6. (2) The six frozen-thawed layers had more observed microbial species and distinct β diversity compared to the unfrozen CK, and the OTU-based co-occurrence network of the soil bacteria in the T1 was apparently better interconnected than that in the T6. However, the outer layers released significantly less CO 2 on average than the CK and inner layers over the seven days of incubation. Although cautions must be taken in extrapolating our results to field scale processes, our study was the first (to our knowledge) to distinguish the heterogeneity of soil inter-layer microbial properties during progressive thawing. Our findings collectively suggest progressive thawing may introduce a non-negligible but long-neglected heterogeneity in carbon biogeochemistry along slopes. [ABSTRACT FROM AUTHOR]

• The soil sensitivity to erosion differed depending on the erosive force applied. • Different soil properties affected the soil sensitivity for water and wind erosion. • The sensitivity of the soils to erosion was higher for wind than for water erosion. Erosion by water and wind can seriously deteriorate soil quality. Traditionally, these two types of erosion have been studied and modelled separately. The main goal of this study was to explore the sensitivity of two Mediterranean soils to both water and wind erosion, in terms of their properties and aggregation. Targeted laboratory experiments were performed using wind and rainfall simulators. Different soil properties and aggregation indices were analyzed for each soil sample. Comparing the rates of soil loss to water and wind erosion revealed an opposite trend in soil sensitivity to these erosional forces; the soil that was most sensitive to erosion by one force was least sensitive to erosion by the other force. This indicates that soil erosion is strongly dependent on the erosive force (water or wind). Therefore, soil erodibility cannot be an unequivocal definition for a certain type of soil, but rather depends on the erosional force applied. Our results also demonstrate that different soil properties affect the size and stability of soil aggregates, controlling the rate of soil loss to water erosion or wind erosion. Under rainfall simulations, the sodium adsorption ratio (SAR) was the main factor controlling soil sensitivity to water erosion (r 2 = 0.76), while loose erodible material (LEM) was the only factor controlling soil sensitivity to wind erosion (r 2 = 0.69). Since dynamic soil properties (e.g., LEM) tend to change over shorter periods of time than intrinsic soil properties (e.g., SAR), the potential for a general increase in the sensitivity of Mediterranean soils to wind erosion processes is expected to be greater than the potential for a general increase in the sensitivity of these soils to water erosion. The calculation of a sensitivity-normalized value for each soil sample revealed that the examined soils were more sensitive to wind erosion than to water erosion. [ABSTRACT FROM AUTHOR]

• Vegetation restoration enhances soil infiltrability and preferential flow. • Soil moisture and total porosity are the dominant factors affecting soil infiltrability. • Macroporosity plays a major role in influencing the degree of preferential flow. Soil infiltration plays a critical role in soil hydrological processes. Land use/cover changes are generally considered to influence soil infiltration. However, the effect of long-term vegetation restoration on the soil infiltration capacity and infiltration pattern is poorly understood. In the present study, we analyzed the infiltration capacity with a double ring infiltrometer and detected the degree of preferential flow using a dye tracer in a typical loess hilly gully catchment of China. Additionally, we identified the relationships between soil characteristics and infiltration capacity and preferential flow. The results showed that (1) converting cropland to forest, shrubland and grassland generally enhanced the soil infiltration capacity. Compared with cropland, the steady-state infiltration rate (SIR) and saturated hydraulic conductivity (K s) increased by 135 % and 155 % in shrubland, by 76 % and 91 % in forest, and by 22 % and 23 % in grassland. (2) Land use changes markedly increased the degree of preferential flow, following the order of shrubland > forest > grassland > cropland. (3) The decline in soil moisture (SM) and bulk density (BD) and the increase in total porosity (TP), macroporosity (MP) and soil organic matter (SOM) could cause higher infiltration capacity and preferential flow. SM and TP were the dominant factors affecting soil infiltrability, while MP was the greatest contributor to variations in preferential flow. Our findings demonstrated that vegetation restoration had a positive impact on soil infiltrability and preferential flow. This effect should be considered when assessing the influence of vegetation restoration on water resources in the Loess Plateau and other arid and semiarid regions. [ABSTRACT FROM AUTHOR]

• Soil infiltration and water flow paths were quantified in subtropical forest types; • Soil water infiltrability rate increased with forest succession; • The degree of soil preferential flow did not evolve along succession sequence; • Soil porosity, root systems and rocks jointly affect soil water flow patterns. Maintaining and improving the water conservation capacity of forest ecosystems is an important step in building regional ecological protection barrier. At present, there is a lack of knowledge about the patterns of soil water flow in different stages of forest succession. Therefore, this study quantified the change tendency of soil infiltration and water flow paths in subtropical different forest types, including pine forests (PF), mixed pine and broadleaf forests (MF) and monsoon evergreen broadleaf forests (BF), and analysed the effect of soil physical properties on hydraulic properties. Results showed that (1) both BF and MF were characterized by a smaller bulk density and the larger porosity than PF. (2) The saturated hydraulic conductivity of BF and MF was 2.1 times and 3.1 times higher than that of PF, respectively, showing that there were clear differences in the soil infiltrability resistance of the different forest types. The observed soil water exchange amount also showed that both BF and MF had higher water holding capacity than PF. (3) Macropore flow and lateral flow were the dominant preferential flow behaviors, but the degree of preferential flow did not evolve along succession sequence PF, MF and BF. The pattern of soil water flow was found to show obvious spatial variability, restricted by the joint influence of soil porosity, root systems and rocks. The above results suggest that soil infiltration improve with the sequence of forest succession, but that soil water flow patterns may be independent of forest succession due to the complex conditions of the soil. This study provided effective data information of forest soil hydrological antecedents. [ABSTRACT FROM AUTHOR]

• There was no significant correlation between soil fungal and bacterial a-diversity and elevation. • Soil temperature (ST), soil water content (SWC), and total phosphorus (TP) were the driving factors affecting the elevation distribution pattern of soil fungal communities. • Soil fungi were more sensitive than bacteria in response to elevation changes. • The network complexity of soil bacteria is higher than that of fungi. The Qinghai-Tibet Plateau is one of the most sensitive regions in response to global climate change. Because soil bacteria have a considerable influence on ecosystem function, it is essential to understand their responses to different climates. We investigated the effects of elevation change on soil microbial diversity and community structure in the Abies georgei var. smithii forest of the Sygera Mountains in southeastern Tibet. We sampled soils from 0 to 10 cm depth at 3500 m, 3900 m and 4300 m asl, and examined changes in fungal and bacterial communities using Illumina MiSeq sequencing. The results showed that 1) fungal and bacterial diversity (Shannon index) did not change significantly (P > 0.05) with increasing elevation, and 2) elevation had no effect on the community structure of bacteria but had a significant effect on the community structure of fungi. Redundancy analysis showed that elevation, soil temperature (ST), soil water content (SWC), and total phosphorus (TP) were drivers of changes in fungal community structure. 3) Elevation had no significant effect (P > 0.05) on the relative abundance of the dominant bacterial phylum in the soil but had a significant effect (P < 0.05) on the relative abundance of the dominant fungal phylum. The dominant bacterial phyla were Proteobacteria, Actinobacteria, Acidobacteria, and Choroflexi, whereas the dominant fungal phyla were Basidiomycota, Ascomycota and Mortierllomycota. The relative abundance of Basidiomycota at 3900 m was significantly higher (P < 0.05) than that of Ascomycota at 3500 m and 4300 m, while the relative abundance of Ascomycota at 4300 m was significantly lower (P < 0.05) than that of Basidiomycota at 3500 m and 4300 m. and 4) the complexity of the bacterial network was the lowest at 3900 m elevation, while the most complex at 3500 m elevation. The fungal network complexity was lower than that of the bacteria. In conclusion, soil fungal communities are more sensitive to changes in elevation than are bacterial communities. [ABSTRACT FROM AUTHOR]

• N addition enhanced soil N immobilization over all seasons. • N addition impacts on soil C sequestration depended upon seasons. • Factors regulating the soil C min and N min rates in response to N addition were seasonally variable. • Soil C min and N min rates became decoupled with N addition for most seasons. Elevated atmospheric N deposition can profoundly alter soil carbon (C) mineralization (C min) and nitrogen (N) mineralization (N min), which could severely impact long-term productivity of grassland ecosystem. However, little is known about how N addition, season, and their interaction affect soil C min and N min rates and their relationships by regulating soil abiotic and biotic factors. Here we investigated the seasonal variations in soil C min and N min rates and their relationship in response to multi-level N additions in a semiarid grassland in 2014–2015, and further identified direct and indirect pathways by which soil abiotic and biotic factors regulated these variations using structural equation modeling. We documented the statistically significant impacts of N addition and its interaction with season on soil C min rates. In contrast, only a significant seasonal effect on the soil N min rate was observed. Random forest analysis revealed that across all seasons, dissolved organic carbon (DOC), soil water content (SWC), catalase, urease, sucrase, microbial biomass carbon (MBC), soil organic carbon (SOC) to total nitrogen (TN) ratio, and TN were the most pivotal predictors of the soil C min rate. Comparatively, catalase, MBC, DOC, NO 3 –-N, urease, TN, NH 4 +-N, SWC, and the MBC to microbial biomass nitrogen (MBN) ratio were the most dominant drivers of the soil N min rate. SEM results indicated that the identified potential drivers that regulated the soil C min and N min rates in response to N addition varied seasonally. Additionally, N addition decoupled the soil C min and N min rates, which was a consistent relationship among most seasons. In summary, our results show that, in this semiarid grassland, current N additions can enhance soil N immobilization across all seasons; however, its impacts on soil C sequestration were seasonally variable. These findings provide evidence that season and its interactions with elevated atmospheric N deposition have important implications for the grassland biogeochemical cycling. [ABSTRACT FROM AUTHOR]

[Display omitted] • A field experiment with rock fragment content (RFC, V/V) from 0% to 75%. • Increasing RFC declined soil nutrient status. • Plants promoted certain soil nutrients and exerted disparate impacts on soil nutrient stoichiometry. • Soil nutrient stoichiometry were mainly shaped by soil structure, soil moisture and plant growth in rocky soils. Soil nutrient contents and stoichiometric ratios are determinants for soil biogeochemical cycling and functions. Variable rock fragment contents (RFC) may shape the soil nutrient status and availability in mountain ecosystems. We need to better understand how and why soil nutrients and stoichiometry shift across the RFC gradients. To investigate patterns of soil nutrient stoichiometry and underlying mechanisms in rocky soils, we conducted a field experiment involving four RFCs gradients (0%, 25%, 50% and 75%, V/V) and five vegetation treatments (four indigenous species, Artemisia vestita , Bauhinia brachycarpa , Cotinus szechuanensis and Sophora davidii , plus a non-planted treatment). Soil total carbon (C), total nitrogen (N), total phosphorus (P) and their molar ratios were measured. The contents of soil C, N and P, and C:N, C:P and N:P decreased with increasing RFC in all treatments, despite their trends were inconsistent in certain soil layers. The averages of soil N content significantly increased by 13.8% and 14.8% in C. szechuanensis and S. davidii , respectively. A. vestita and B. brachycarpa had higher soil C:N than C. szechuanensis and S. davidii. Soil nutrients and stoichiometry were positively related to soil water content (SWC) and soil capillary porosity, and negatively to bulk density and soil non-capillary porosity in all vegetation treatments, but varying relationships with biomass of plant components. These results demonstrated negative effect of RFC and discrepant effects of the plants on soil nutrients and stoichiometry. Soil structure, SWC and vegetation were the main drivers of variations in soil nutrient stoichiometry. We further concluded that soil nutrient stoichiometry in rocky soils is shaped by two influencing paths; effects of RFC on soil physical properties (SWC and soil structure) and effects of different vegetations. Our findings advance knowledge and mechanisms of soil nutrient stoichiometry in rocky soils and provide theoretical support for improving and restoring nutrient status in stony regions. [ABSTRACT FROM AUTHOR]

[Display omitted] • The CAST model well simulated the effect of fertilization practices on carbon dynamics in a chronosequence; • Free microaggregates in the Fluvaquent were the primary C sequestration fraction under RCP2.6 scenarios; • MNPK treatment promotes C storage in the study soil under current and future climates. Quantifying soil structural dynamics and aggregate turnover is important in understanding soil organic carbon (SOC) stocks, particularly over decadal and larger time scales. Until now it has remained unclear clear how soil aggregate size and its associated carbon respond to both long-term soil fertility and climate change. Here, we explore changes in soil structure and aggregate organic C (OC) stocks under different fertilization practices by combining field chronosequence SOC measurements with dynamic and process modeling in a long-term wheat-maize field experiment on the North China Plain. The fertilization practices comprise no fertilization (CK), chemical fertilization (NPK), and combined manure and NPK treatments (MNPK). The experimental measurements included the mass of OC stocks in different soil aggregate size classes. We used this information to calibrate parameters of the Carbon, Aggregation, and Structure Turnover (CAST) model and to predict future changes in aggregate structure and the resulting OC stocks using the RCP2.6 scenarios that were defined by the outputs of five future climate models from IPCC projection. With trends towards a wetter climate and increasing soil moisture under the RCP2.6 scenarios for the region, soil OC stocks will increase in all three treatments, with the strongest increase under MNPK due to exogenous C inputs. The CAST model output further suggests that changes in microaggregate (250–53 μm) OC stocks in the NPK and MNPK treatments accounted for 78.6 % and 75.3 % of the calculated change in total SOC stocks between the early and late 21st century. In conclusion, our combined data and modeling approach describes changes in soil aggregate C, identifies the primary soil aggregate size class of microaggregates involved in C sequestration in an agricultural soil, and predicts the role of Fluvaquent soils on the North China Plain as a future C sink. [ABSTRACT FROM AUTHOR]

• Soil infiltrability was differentially regulated by soil texture and plant roots. • The variations in regional soil infiltrability were more explained by soil texture. • Various root-soil combinations differentially affected regional soil infiltrability. • Soil texture had the strongest total effect on soil infiltrability on a reginal scale. Soil infiltrability controls precipitation input to soil and plays a crucial role in regulating soil eco-hydrological processes and ecosystem production in water-limited areas worldwide. The effects of root traits on soil infiltrability have been widely investigated at individual sites, but root-soil interactions and their effects on soil water infiltration over large spatial scales remain poorly understood. This study aimed to identify the unique characteristics of soil infiltration processes and different contributions of soil texture and root morphological traits to soil infiltrability. For this purpose, 153 plots of natural revegetated land with two contrasting plant species (Artemisia gmelinii Web. with tap root systems and Stipa bungeana Trin. with fibrous root systems) and bare land were selected in three regions along a texture gradient in the Loess Plateau of China. The results showed a distinct spatial variability of soil infiltration rates across the three regions with soil texture explaining the variability more strongly than plant species at several infiltration stages. Rooted soils had higher infiltration rates than bare soils, with nonsignificant inter-species difference under three soil texture types. Furthermore, soil texture and root morphological traits explained 92.03% and 74.75% of the total variance of soil properties (soil organic matter, aggregate stability, and soil porosity), and their interaction effects (73.09%), accounted for a considerable proportion. These findings suggest that soil texture and root morphological traits indirectly affect soil infiltrability by modulating soil properties, with soil texture having a higher contribution. In addition, the effects of root morphological traits on soil infiltrability were found to be dependent of soil texture on the regional scale. Therefore, the effects of soil texture and root-soil interaction deserves further attention in assessing soil hydrological processes on large spatial scales in the future. [ABSTRACT FROM AUTHOR]

• The freeze–thaw cycle affected the soil hydrological process in active layer; • There were significant differences in soil hydrothermal processes at the slope scales and profile scales; • The redistribution of soil water during the freezing and thawing periods is affected by vegetation." The Qinghai-Tibet Plateau (QTP) is a region with an extensive area of permafrost that is very sensitive to climate change. In this study, soil water and thermal dynamic processes in the active layer of the QTP permafrost area at the profile and slope scales were investigated. The results showed that the hydrothermal process in the active layer soil was strongly affected by freezing and thawing processes and external weather conditions. The temperature of the active layer fluctuated in tandem with air temperature. The soil water content was more stable during the freezing period and showed a "double-hump" trend during the thawing period. The correlation coefficient between soil and air temperature decreased with depth, from 0.896 in the surface soil layer to 0.082 in the deep soil layer; and the correlation coefficient between unfrozen water content and soil temperature during the freezing period showed an overall increasing trend with depth. The soil layers at different depths at the top and bottom of slope profiles differed in their hydrothermal processes due to the physicochemical properties and texture of the soil and vegetation types. The water-heat exchange of the surface soil is more frequent than that of the deep soil, and the frequency is more at the bottom than at the top of the slope. The soil water content at a depth of 0.25 m was the highest in the profile in association with a higher organic matter content and the blocking effect of dense roots. The changes of soil hydrothermal process in the active layer accelerated the hydrological cycle and the spatial–temporal variability in water resources in the frozen soil area. These effects might lead to a series of ecological and environmental problems, such as permafrost degradation and desertification in the QTP alpine meadow ecosystem. [ABSTRACT FROM AUTHOR]

• Soil carbon release was evaluated in a Caragana korshinskii plantation after extreme rainfall events. • Extreme rainfall changes significantly affected the soil carbon release. • Soil carbon release increases with soil depth over the period of extreme rainfall events. • Temperature sensitivity only increased at 10 cm soil depth after extreme rainfall due to the pulsed soil carbon release. • Unstable soil carbon release after extreme rainfall events can affect the soil carbon cycle. Projected increases in the frequency and magnitude of extreme rainfall events can profoundly impact terrestrial ecosystems. However, the response of soil carbon release (RS) at various depths to these events and associated regulatory processes has not been well-documented in small watersheds. We measured the mean CO 2 concentration, soil moisture (SM), and soil temperature (ST) at depths of 10, 50, and 100 cm in situ before and after extreme rainfall events between June and September 2019, in a typical small watershed of the Loess Hilly Region, China. RS, calculated using Fick's first law in one dimension, revealed the relationships between RS and extreme rainfall events. During the study period, we screened four extreme rainfall events, of which three were used. The mean RS at 10, 50, and 100 cm soil depths after extreme rainfall (post-RS) were significantly higher than those before (pro-RS) (P < 0.05). Simultaneously, decreased ST at a depth of 10 cm and increased SM at a depth of 10 cm during periods of extreme rainfall contributed to decreased RS at a depth of 10 cm. By contrast, the RS at depths of 50 and 100 cm were enhanced during periods of extreme rainfall and peaked between days two and four after the extreme rainfall events due to the significant stimulating increase in SM (P < 0.05); the relative change in RS at 50 cm soil depth was the largest. Moreover, the RS values at three soil depths were changed by extreme rainfall events (with higher SM to RS), yet the R 2 of the ST was lower after extreme rainfall. In addition, after extreme rainfall, the temperature sensitivity (Q 10) increased at a depth of 10 cm, while it decreased at depths of 50 and 100 cm. These findings imply that more CO 2 is released from deep soil in semi-arid shrubs under extreme rainfall events with sustained increase for 2–4 days. The results will help predict the impact of future climate change on regional carbon emissions and improve the accuracy of predictive model. [ABSTRACT FROM AUTHOR]

• Forestland had significantly lower soil water contents than grassland. • Different vegetation restoration types altered the soil texture. • Afforestation promoted the formation of deep roots. • Forestland did not increase SOC content in the soil profile. • Apple orchard had significantly lower MWD than the others. Vegetation restoration on the Loess Plateau has decreased soil erosion. However, the comprehensive effects of different vegetation restoration types on soil properties are not clear. Evaluating the soil properties of the main economic and ecological tree species on the Loess Plateau can provide crucial guidance for regional ecological environment restoration. Therefore, we compared soil water content (SWC), soil particle composition, root distribution, soil organic carbon (SOC) content, soil bulk density (BD), total porosity (TP), saturated hydraulic conductivity (Ks), soil water retention curves (SWRCs), and soil aggregate stability of peach (Prunus persica), walnut (Juglans regia L.), and apple (Malus pumila) orchards, black locust (Robinia pseudoacacia), and grassland of similar age on the semi-arid Loess Plateau. Forestland, especially black locust, had significantly lower SWC than grassland. The different vegetation restoration types altered the soil texture; grassland had the highest clay content, while black locust had the lowest. Afforestation promoted deep root formation, reaching>10 m, with>50 % of the roots below 2 m. Compared with grassland, forestland did not increase SOC content in the soil profile. Soil BD increased with increasing soil depth from 0 to 80 cm for the five vegetation types but was relatively stable below 80 cm; grassland had the greatest BD, while black locust had the lowest. The walnut orchard had the lowest Ks in the 0–80 cm soil layer. The apple orchard had the highest residual soil water content and field capacity. The apple orchard had significantly lower mean weight diameter (MWD) than the others, indicating low surface soil stability due to tillage management, increasing the risk of soil erosion. Overall, these results suggested that black locust had greater negative effects on soil properties than economic trees. Therefore, black locust establishment or planting density should be reduced in future vegetation restoration processes. [ABSTRACT FROM AUTHOR]

Soil water content (SWC) is a critical variable in studies of hydrological processes and the soil–plant–atmosphere continuum, especially in arid and semi-arid regions such as the Loess Plateau. Knowledge of the effects of vegetation types on soil water dynamics would aid in understanding the mechanisms responsible for water shortages and addressing the problem of poor long-term vegetation recovery. To evaluate the response of soil water storage (SWS) to different land use types during long-term natural vegetation succession, we examined soil moisture under different land use types (grassland, shrubland and forestland) at different times (2005 and 2014) in the Ziwuling forest region, located in the central part of the Loess Plateau, China. Our results showed that vegetation type had a significant effect on SWS in the 0–500 cm soil layer. The SWS in grassland and shrubland was significantly higher in August 2014 than in August 2005, but the pattern was reversed for forestland. In the same year, the SWS was highest in grassland, intermediate in shrubland, and lowest in forestland. SWS and SWC showed a highly significant and positive relationship in the 0–60 cm soil layers ( P < 0.01), and both soil bulk density (BD) and soil total nitrogen (TN) showed a significant relationship with SWS. In addition, the SWC and soil total porosity (TP) showed a significant positive relationship in the 0–20 cm soil layer ( P < 0.05). These results are expected to provide insights into land water management and inform efforts to estimate the productivity and sustainability of semiarid ecosystems. [ABSTRACT FROM AUTHOR]

Rock outcrop ecosystems, such as limestone cedar glades (LCGs), are known for their rare and endemic plant species adapted to high levels of abiotic stress. Soils in LCGs are thin (< 25 cm), soil-moisture conditions fluctuate seasonally between xeric and saturated, and summer soil temperatures commonly exceed 48 °C. The effects of these stressors on soil microbial communities (SMC) remain largely unstudied, despite the importance of SMC-plant interactions in regulating the structure and function of terrestrial ecosystems. SMC profiles and functional diversity were characterized in LCGs using community level physiological profiling (CLPP) and plate-dilution frequency assays (PDFA). Most-probable number (MPN) estimates and microbial substrate-utilization diversity (H) were positively related to soil thickness, soil organic matter (OM), soil water content, and vegetation density, and were diminished in alkaline soil relative to circumneutral soil. Soil nitrate showed no relationship to SMCs, suggesting lack of N-limitation. Canonical correlation analysis indicated strong correlations between microbial CLPP patterns and several physical and chemical properties of soil, primarily temperature at the ground surface and at 4-cm depth, and secondarily soil-water content, enabling differentiation by season. Thus, it was demonstrated that several well-described abiotic determinants of plant community structure in this ecosystem are also reflected in SMC profiles. [ABSTRACT FROM AUTHOR]

Wetlands supported by groundwater in semiarid regions are extremely vulnerable to the impacts of droughts, particularly anthropized systems. During drying periods, soil water content arises as the controlling factor for environmental and ecological disturbances such as the spread of invasive plant species, the combustibility of organic soils, nutrient redistribution or soil physical disruption. The presented management tool for semiarid wetlands is supported by the Soil-Water-Atmosphere-Plant (SWAP) model for soil moisture modeling and simulation. Main input data are experimental values of soil physical and hydraulic characteristics, soil moisture measurements, vegetation growth parameters and climatic records. Decision-makers can use the calibrated datasets to predict the evolution of soil moisture under different drying scenarios in order to choose the most efficient management options for preventing soil moisture to reach critical values. The approach has been tested in the anthropized Mediterranean semiarid wetland area of Las Tablas de Daimiel National Park in central Spain. Ten vadose zone water models were successfully calibrated and validated for different soil units. Critical soil moisture conditions for invasive reed overgrowth and peat combustibility have been estimated. Simulations of a typical 2-year drought scenario indicated that critical soil moisture conditions for reed overgrowth are attained 9–10 months after flooding ceased and that peat areas colonized by reed plants become combustible (even 50% probability chance) by the end of the simulated period. [ABSTRACT FROM AUTHOR]

Soil water repellency (SWR) has been reported under different soils, land uses and regions of the world, particularly in forest land and after wildfires, yet the understanding of this variable in agricultural lands is still rather limited. This study presents the characterization from field-based measurements of SWR in four contrasted olive groves ( Olea europaea L.) in Spain in terms of different environmental conditions and management: abandoned and commercial farms under permanent cover crop, conventional tillage and herbicide use. The main objectives were [1] to evaluate the potential occurrence, intensity and persistence of soil water repellency in different types of olive groves and [2] to explore its spatio-temporal features as well as the influence of soil properties such as organic matter (OM) and soil moisture. The Water Drop Penetration Time test (WDPT) was used in situ to assess SWR values. Measurements were carried out in two areas for each of the four groves: below and between the tree canopies. A high spatial and seasonal variability was observed. SWR was absent (WDPT = 0 s) for the olive groves under conventional tillage and with the lowest values of OM (OM-mean = 2.04%). The maximum WDPT values were found for cover crop under canopy in summer (WDPT-max = 610 s) and on the lanes in autumn (WDPT-max = 468 s). SWR was developed during the dry season, and to be reduced during the rainfall season as the organic compounds might be reoriented and turned amphiphilic. Strong water repellent values (> 60 s) were related with extremely high OM values (> 12%) for the cover crop orchard. [ABSTRACT FROM AUTHOR]

Plant litter can be incorporated into topsoil under natural circumstances by soil splash, sediment deposition, and soil-dwelling animal activities. The incorporated litter can change the mechanical properties of soil and the decomposition of the incorporated litter can improve soil structural stability. Those changes likely influence soil detachment process by overland flow. This study was undertaken to quantify the effects of incorporated plant litters into topsoil on the temporal variation in soil resistance to detachment by overland flow using natural soil samples collected from four different plots (one control and three litter incorporation treatments) and then scoured under six different flow shear stresses in a hydraulic flume. The experiment started from April 19 to October 5, 2015 for 10 times at approximately 20 days sampling intervals. Soil properties and environmental parameters were also measured at each sampling time to explain the temporal variations in rill erodibility and critical shear stress. The results showed that the incorporated plant litter was effective to enhance soil resistance to flowing water erosion. Compared to bare soil, rill erodibilities of litter incorporated soils of black locust, sea buckthorn, and green bristle grass decreased by 24.3%, 33.5%, and 34.8%. The temporal variations in rill erodibility of bare and litter incorporated soils were similar. Rill erodibility decreased significantly over time as an exponential function for both bare and litter incorporated soils. The relative rill erodibility of three litter incorporated soils increased over time as a power function. The fitted critical shear stress increased exponentially over time. The temporal variations in rill erodibility could be explained by the temporal variations in soil consolidation, water stable aggregate, and litter decomposition. Rill erodibility could be well estimated by soil bulk density, water stable aggregate, and litter mass density ( r 2 = 0.92). [ABSTRACT FROM AUTHOR]

Drylands are important ecosystems that are facing severe challenges under a changing climate. The relationships between soil moisture and vegetation have garnered international interest because of their significant impact on ecosystem restoration in semi-arid and arid regions. Grasslands are among the largest ecosystems in the world and are very important to dryland ecosystems. The Loess Plateau in China is an important example of drylands, and grasslands occupy more than 1/3 of its area. Water is the primary limiting factor of vegetation restoration, so understanding the relationship between grasslands and soil moisture on the Loess Plateau is imperative. The processes of precipitation, soil surface infiltration and evaporation, root water uptake and leaf transpiration are important for the relationship between grasslands and soil moisture. This paper found the following research topics that were related to the Loess Plateau based on 283 references of local studies from CNKI, ScienceDirect and Springer: (1) the effects of grasslands on soil moisture, including the influence of precipitation, geography, grassland type, grass age and growth stage on soil moisture and soil moisture determination methods; (2) the influence of soil moisture on grasslands, including the influence of soil moisture stress on grass growth and the methods for determining the physiological and ecological characteristics of grass; and (3) models of the relationships between grasslands and soil moisture. International references were used to explain certain processes and were compared with studies on Loess Plateau. Existing studies on the Loess Plateau paid more attention to these phenomena compared to water transport processes. Additional process-based studies with greater accuracy, longer time series, and larger spatial scales are needed to achieve ecosystem sustainability on the Loess Plateau. This summary of studies on the Loess Plateau may provide examples for research on arid and semi-arid areas in other countries. [ABSTRACT FROM AUTHOR]

Water erosion is the main cause of soil degradation on cultivated lands under Mediterranean climate. In these conditions, ephemeral gully erosion (EGE) is a major contributor to loss of soil productivity due to the big amounts of soil removed from the most productive top-layer. However, only a few studies on the effects of EGE and artificial controlling measures on soil degradation are available. The objective of this study was to assess the impact of EGE combined with soil infilling by tillage on several physicochemical soil properties related to soil fertility and productivity through the calculation of a soil quality index (SQI) by means of a statistical approach. It was hypothesized that the sites affected by this process of erosion and infilling of ephemeral gullies (EGs) exhibit considerable changes in the soil properties compared with locations that do not undergo this process. The study site consisted of 5 fields with contrasting soil properties which have been continuously cultivated with winter wheat. The site, located in the internal area of Sicily (Italy), represented a typical Mediterranean arable land and was severely affected by EGE. A set of soil samples were collected to investigate the spatial variation of the SQI across each location: 12 sample points in the EGE area; 4 samples in the deposition zone; 4 reference points in the area unaffected by EGE. The SQI was estimated by closely monitoring a set of main chemical and physical soil variables which influence soil fertility status: particle size (sand, silt and clay content), bulk density, gravimetric moisture, pH, electrical conductivity, carbon content (inorganic, organic and total), nitrogen content (ammonium, nitrate and total) and available phosphorus. The results showed that channelized erosion posed a threat to soil quality status even at a single cultivated field's level; therefore, the soil's ability to sustain crop production is expected to be compromised in the long run. Reductions of the SQI were observed at the EGs system area and at the deposition area in every EGs. Besides that, the lowest values of SQI were obtained inside the EGs channel and in the nearby soil areas, which were generally used to fill those channels. Soil degradation occurred in the areas which were subjected to EGE and infilling process, with key soil properties being clay (CC), sand (SaC), silt (SiC), and total organic carbon (TOC) contents. This approach helps to understand the impacts of EGE and its controlling measures on soil degradation in Mediterranean agricultural fields. [ABSTRACT FROM AUTHOR]

• High-frequency extreme rainfall promotes the carbon sink function of wet meadows. • Increase in extreme rainfall frequency affects soil properties and promotes CO 2 absorption. • The increase in extreme rainfall frequency increases aboveground net primary productivity. • The increase in extreme rainfall frequency decreases soil bulk density. • The CO 2 flux was affected by soil carbon components under different extreme rainfall frequency. Extreme rainfall amount and frequency can alter carbon dioxide (CO 2) exchange between the soil and vegetation in wetlands. Seasonal redistribution of extreme rainfall events is one component of a hydrological regime that affects soil water content (SWC), but its impacts on ecosystem CO 2 exchange in the Qinghai-Tibet Plateau (QTP) wetlands remain unclear. Here, we conducted field simulation experiments to understand the effects of extreme rainfall with high to low frequency once every-one, two, three, and four weeks on CO 2 exchange of wet meadow ecosystem in QTP. The ecosystem absorbed more CO 2 with high-frequency extreme rainfall (−1468.52 mg C m-2h−1) than with current natural amounts and frequency of rainfall (−1162.51 mg C m-2h−1) throughout local vegetation growing seasons. However, under low-frequency extreme rainfall (−916.72 mg C m-2h−1) the wetland absorbed less CO 2 than under natural rainfall frequency. This difference comes from the changes in net ecosystem productivity (NEP) and ecosystem respiration (ER) in wet meadows due to soil temperature (ST) and soil nutrient content. In the rapid growth stage of plants, ER and NEP exhibited single-peak curves due to increases in ST and SWC, and they reached their maximum values in August. Our results indicate that the distribution pattern of extreme rainfall events plays a critical role in regulating ecosystem CO 2 exchange in the wet meadows of the QTP. More research on the related changes between contents of soil nutrient contents and extreme rainfall events could improve the accuracy of C budget estimation in wet meadows. The predicted regional impacts of future climate extremes of rainfall will rely on changes in their frequency and timing. [ABSTRACT FROM AUTHOR]

• Soil clay and moisture mediate the decoupling of C, N and P cycling along an elevational gradient. • Total organic C pools were highest where the clay content was highest. • Soil organic N pools were controlled by clay and soil moisture effects on microbial stabilisation. • Soil P pools were not related to clay and soil moisture. • Soil organic P was decoupled from soil organic C and N pools along the hillslope. Grasslands extend across a variety of topographies including non-flat hilly areas with varied soil texture and moisture that can mediate soil biogeochemical cycling of carbon (C), nitrogen (N) and phosphorus (P). In this study we examined soil organic C, total N and P pools (both inorganic and organic), as well as gross N mineralisation (GNM, as a measure of microbial activity and N dynamics) and microbial C, N and P in winter and spring along a grassland hillslope. Our results showed that variation in soil clay and associated soil moisture were the most important mediators affecting C and N dynamics along the grassland elevational gradient. Total organic C pools were highest where the clay content was highest, likely because of the sorption capacity of clay stabilising organic matter against microbial decomposition. Likewise, the variation in soil organic N pools along the hillslope was mostly controlled by clay and soil moisture effects on microbial stabilisation of organic N. Furthermore, microbial C, N and GNM increased with increased soil moisture, suggesting that microbial activity was limited by soil moisture. In contrast, soil P pools were not related to clay and soil moisture, while soil organic P was decoupled from soil organic C and N pools along the hillslope. Possibly, differences in microbial stabilisation and mineralisation pathways (oxidation for C and N, hydrolysis for P), microbial homeostatic regulation of C, N and P, and P fixation resulted in a decoupling of P from C and N cycling in this grassland. We conclude that variation in clay and associated soil moisture along grassland hillslopes can have important but non-unidirectional effects on soil C, N and P cycling. [ABSTRACT FROM AUTHOR]

• Shrub encroachment in alpine meadows on soil pH were examined. • Shrub encroachment changed soil porosity structure of in alpine meadow. • Shrub encroachment increased soil water and salt upward transport. • Shrub encroachment increased the potential risk of salinization. Alpine meadows are undergoing shrub encroachment due to climate change and human activities, which affects the health of alpine meadow ecosystems. Previous studies mostly focused on the impact of shrub encroachment on vegetation communities, but few studies were focused on the impact of shrub encroachment on soil pH. This study shed light on this topic by measuring soil moisture and water holding capacity under different levels of shrub encroachment (shrub coverage ranging from 8% to 90%) in alpine meadows located on the Qinghai-Tibet Plateau. Results showed that the intensification of shrub encroachment increased soil saturated water content, soil capillary moisture capacity and soil field capacity, but decreased soil moisture at the uppermost soil layer (0–10 cm). The increase of soil saturated water content and soil capillary moisture capacity increased soil pH. The intensification of shrub encroachment increased soil pH at soil depth of 0–10 cm, but decreased soil pH at soil depth of 20–30 cm. Overall, shrub encroachment could increase soil water and salt upward transport by reducing soil moisture and enhancing soil capillary moisture capacity, resulting in an increase of soil pH. These findings are conducive to better understand the impact of shrub encroachment on the redistribution of soil salinity in alpine meadows, and can provide a theoretical basis for predicting the changes of alpine meadow community facing future climatic change and human activities. [ABSTRACT FROM AUTHOR]

• Trade-offs between SMC and species diversity are lowest for natural grasslands. • Species diversity of afforested land in the steppe zone is at the expense of SMC. • The SMC of afforestation lands in the forest zone can maintain existing species diversity. • The trade-offs between SMC and species diversity are balanced for the forest steppe zone. Soil moisture and plant species diversity are key factors determining the structure, function and stability of terrestrial ecosystems in arid and semiarid environments. However, the relationship between species diversity and soil moisture of different vegetation restoration measures over a precipitation gradient has not been thoroughly explored, inhibiting decision-makers' ability to formulate vegetation restoration policies. In this study, we examined the relationship between the soil moisture content (SMC) and species diversity of two vegetation restoration measures (afforested lands and natural restoration grassland) in different vegetation zones (steppe, forest-steppe and forest) on the Loess Plateau. The results showed that the species diversity of afforested lands was ranked as forest zone < forest-steppe zone < steppe zone, which contrasts with natural grasslands. The average SMC of afforested lands was ranked as steppe zone < forest-steppe zone < forest zone, and the results further indicated afforestation decreased SMC compared with the natural grassland. The relative benefit of the species diversity index in afforested land was more extensive than that of soil moisture in the steppe zone but smaller in the forest zone, and the trade-offs between soil moisture and species diversity were smallest in the forest-steppe zone but approached no trade-offs in natural grasslands. Our study suggests that although natural grassland is the ideal ecosystem across all the vegetation zones examined, the forest and forest-steppe zones are most suitable for afforestation, accounting for the human need for timber harvesting. However, afforestation plantations need to be thinned appropriately to maintain high soil moisture and species diversity and low trade-offs between soil moisture and species diversity. [ABSTRACT FROM AUTHOR]

• Root reinforcement first increases then decreases with increasing soil water content. • Root reinforcement slightly differs between wetting and drying conditions. • Roots' effectiveness for reinforcement becomes weak when soil moisture increases. • Soil moisture affects root reinforcement by altering the percentage of slipped roots. • Besides tensile strength, root failure mode is key for reinforcement estimation. Plant roots can protect soil against shallow landslides. The mechanics of rooted soil failure under varying soil water content remain poorly understood. The aim of our study was to characterize the impact of soil water content on root mechanical traits and reinforcement to soil. One-year-old Symplocos setchuensis trees were replanted in shear boxes (0.4 × 0.4 × 0.5 m3), which were placed in a canopy gap on Jinyun Mountain, Chongqing, China. After three years of vegetation growth, root mechanical measurements and soil direct shear tests were performed at five levels of volumetric soil water content varying from 14.9 to 44.4 %, by either wetting or drying the soil. For each shear box, we measured soil shear strength, root area ratio, root tensile force, root water content, and root failure mode (slippage versus breakage) during or after the shearing process. Root area ratio and root failure modes were examined for different root diameter classes. With increasing volumetric soil water content, we found a persistent decrease in root tensile strength (ca. 15 %) and an increase in root water content (ca. 11 %), although the dependence on volumetric soil water content was not statistically significant for certain soil water content levels. We found that both additional shear strength of rooted soil and proportion of root failure in breakage increased first and then decreased, with peak values occurring at a soil water content of ca. 22 %. Altered root tensile force (68.0 % contribution to root reinforcement variation) and the change in proportion of root failure modes (breakage or slippage; 8.4 % contribution to root reinforcement variation) jointly contribute to the negative impact of soil water on observed root reinforcement. Soil shear strength was positively correlated with root area ratio and their relationship was linear. At high soil water content (>28 %), the slope of the linear relationship decreased rapidly with increasing soil water content, suggesting that increasing root biomass is not effective for enhancing root reinforcement in very wet soil conditions. Regarding hysteresis, root reinforcement magnitude and efficiency were higher in the drying process than in the wetting process when soil moisture was low. Our results highlight the vital role of soil water features in affecting soil-root mechanical interactions and such effects should be taken into account in future root reinforcement modelling and assessment [ABSTRACT FROM AUTHOR]

• Soil erosion was measured by detecting changes in air–soil interface of TDR probe. • Feasibility of TDR-based soil erosion measurement was evaluated by experiments. • Soil erosion can be effectively measured within a wide soil moisture range. • Simultaneous measurement of soil moisture content can ensure reliability. Scientific research and control technology of soil erosion both rely on accurate and efficient soil erosion measurements. Based on the principles of locating interfaces in layered media and measuring dielectric properties by time domain reflectometry (TDR), we developed TDR-based measurement of changes in the air–soil interface along the TDR probe for soil erosion measurement, and simultaneously measuring volumetric soil moisture content (θ v). Part of a three-rod TDR probe was inserted in the soil and the rest exposed to air, so changes in the air–soil interface could be denoted by changes in the length of exposed probe (L air). TDR waveforms were analyzed using a combination of tangent line method and second-order bounded mean oscillation methods to identify time points at positions of impedance discontinuity in electromagnetic propagation, then converting these data to L air and θ v by calibrated equations. According to the laboratory experiment using sandy loam and silt loam, L air could be effectively measured within a wide soil moisture range by the calibrated equation and the thickness of the eroded soil layer could thus be determined. The RMSE of θ v measurement ranged between 0.003 and 0.025 cm3 cm−3, which enabled the identification of the appropriate soil moisture range for measuring L air , and achieve reliable simultaneous measurement of soil erosion and soil moisture content. The simulated rainfall experiment using sandy loam and silt loam and field scouring experiment conducted in loam also indicated that the proposed method could achieve high measurement accuracy in erosion environments, for which L air with the RMSE from 1.8 to 2.1 mm and θ v with the RMSE from 0.007 to 0.024 cm3 cm−3. The proposed method has various advantages, including versatility, minimal disturbance, easy automation of measurement at multiple positions, etc., could serve as a new technical option for soil erosion measurement, and extend the utilization of TDR. [ABSTRACT FROM AUTHOR]

• Thermal effects on soil hydraulic and mechanical properties were investigated. • An increasing temperature decreased the soil Ψ in the middle stage of SWRC. • The soil cohesion increased as the power function with increasing soil Ψ. • The soil friction angle increased as the linear function with increasing soil Ψ. • The increase in soil temperature decreased soil matric suction and shear strength. The soil hydrologic and mechanical properties play an important role in the slope stability in the red soil hilly region of southern China. In this study, the red soil layers in a collapsing gully wall were used to investigate the effects of temperature on the soil water retention curve (SWRC) and shear strength. The results showed that the SWRCs of the red soil under different temperatures could be accurately described by the van Genuchten (VG) model (R 2 > 0.95, root mean square error (RMSE) < 0.024). An increasing temperature significantly decreased the soil water holding capacity (WHC), especially in the intermediate range of the SWRCs of the red soil. The soil saturated hydraulic conductivity (Ks) increased linearly with temperature. The soil cohesion and soil friction angle decreased by approximately 44.13% and 30.40% respectively when the soil water content increased from 0.24 cm3 cm−3 to 0.42 cm3 cm−3. The mean soil cohesion and soil friction angle decreased approximately 8.56 kPa and 1.34° respectively when the soil temperature increased from 25 °C to 40 °C. Regression analysis showed that the soil cohesion increased as the power function with increasing matric suction (0–2000 kPa), and friction angle increased as the linear function with increasing matric suction. These results illustrated that an increase in temperature will decrease soil matric suction and shear strength but enhance the soil infiltration rate under certain soil moisture levels. Therefore, the stability of a collapsing gully wall will sharply decrease under the conditions of high temperature and heavy rain in summer. [ABSTRACT FROM AUTHOR]

[Display omitted] • Thinning promoted the increase of soil recalcitrant C and stability of SOC pool. • Increase of ligninase activity was associated with soil moisture and temperature. • Thinning induced SOC pool stability was mainly related to soil C-degrading enzyme. Forest thinning greatly affects the soil organic carbon (SOC) pool by changing the soil microenvironment, organic matter input, and microbial metabolism. However, the heterogeneity of thinning intensity, recovery stage, and microclimatic conditions increases uncertainty about the effect of thinning on SOC. The activities of C-degrading enzymes (ligninases and cellulases) secreted by soil microorganisms can be used to explore the effects of thinning on soil C storage. Our meta-analysis showed that forest thinning significantly increased soil temperature (ST), soil moisture (SM), and pH, but significantly decreased litter and fine root biomass. Moderate thinning and recovery time extension increased soil C storage, SOC, and recalcitrant organic C (ROC). An increase in the thinning intensity significantly improved ligninase activity, while decreasing cellulase activity and extending recovery time after thinning. Increased SOC, soil labile organic C (LOC), and ROC with thinning were associated with increased ligninase activity that was significantly positively correlated with soil pH, SM, and ST after thinning. The variation in soil ligninase: cellulase ratio induced by thinning was significantly positively correlated with the increases of soil ROC: LOC ratio and SOC after thinning. Therefore, forest thinning enhanced SOC pool stability through the effect of ligninases and cellulases on SOC sequestration. The global pattern of soil C-degrading enzymes in response to thinning has deepened our understanding of the mechanism by which thinning affects the SOC cycle. [ABSTRACT FROM AUTHOR]

[Display omitted] • Revegetation enhanced SOC mineralization rate in desert region. • Proportion of mineralizable SOC decreased after revegetation. • Temperature sensitivity of SOC mineralization increased with the stand ages. • SOC mineralization was critically related to available phosphorus and C:N ratio and temperature. Revegetation plays a critical role in the soil organic carbon (SOC) cycle, especially in desert regions. However, the effects of this restoration practice on SOC mineralization are poorly understood, which inhibit the accurate estimation of SOC sequestration. In this study, SOC mineralization rates in revegetated sites along a chronosequence in the Tengger Desert were investigated by the incubation method, and the relationships between SOC mineralization rate and the temperature (T) and soil moisture (SM) of incubation, soil properties and vegetation characteristics were analyzed. The results showed that SOC mineralization rates and its temperature sensitivity (Q 10) significantly increased after revegetation. The maximum CO 2 -C emission rates (MR), cumulative CO 2 -C emissions (CCE), potentially mineralizable SOC (C 0) and Q 10 increased by 0.04–5.62, 0.78–4.88, 0.94–4.04 and 0.37–0.47 times in 64 years following revegetation, respectively, while the proportion of C 0 to total SOC (C 0 /SOC) decreased by 2.12–7.22 times. T and SM and their interaction had significant influences on MR, CCE, C 0 and C 0 /SOC, while SM had no significant effect on Q 10. The stepwise multiple linear regression analysis showed that the SOC mineralization rate had greater R2 with stand age and smaller R2 with SM, indicating that the SOC mineralization was mainly regulated by the stand age. The SEMs indicated that the soil properties were the main direct factors affecting SOC mineralization. The RDA indicated that soil AP, C:N ratio and T were the key factors controlling SOC mineralization during the revegetation process. Our findings indicated that long-term revegetation in desert regions enhanced SOC transformation and its temperature sensitivity, but decreased the percentage of CO 2 -C loss from soil, thus leading to SOC accumulation. [ABSTRACT FROM AUTHOR]

• Two low-cost FDR-TDR devices to measure soil water content are evaluated. • Devices were compared with TDR100 using 2- and 3-rod probes. • Comparations were made in air, distilled water, and in a wetted soil column. • The study was complemented with a field experiment. • Robust estimates of water content were obtained with the two VNA devices. Time Domain Reflectometry (TDR) is a non-destructive technique to determine the soil apparent dielectric constant, ε a , the volumetric water content, θ, and bulk electrical conductivity, σ. However, the high cost of TDR devices may limit its use. This study evaluates two different low-cost Vector Network Analyzers (VNA) commercially available (NanoVNA), with 1.5 (VNA1.5) and 3.0 (VNA3.0) GHz maximum operating frequency. NanoVNA can be used for measurements of Frequency Domain Reflectometry (FDR) or, after suitable post-processing, for θ and σ TDR measures. Although FDR and TDR are dual procedures, TDR is easier to interpret for soil experiments. The TDR waveforms and ε a measured with NanoVNA connected to 10 and 20 cm length three-rod probes immersed in air, distilled water, and a soil column with different θ were compared to those measured using a TDR100 (Campbell Sci.) instrument. The capacity of VNAs to measure σ was evaluated by immersing a 10 cm length three-rod probe in different NaCl-water solutions. Measurements obtained with the VNA and TDR100 were compared in a field test using two-rod 22 cm length TDR probes inserted in soil plots with increasing water content. A robust fit was observed between TDR waveforms registered with the two VNAs and the TDR100. Although VNA3.0 doubles the frequency range of VNA1.5, both devices allowed for good estimates of ε a (ε aVNA1.5, 3.0 = 1.001 ε aTDR100 – 0.2125; R2 = 0.999). These results indicate that the low-cost VNA devices can measure soil water content with similar accuracy and precision as the TDR100. A good agreement (σ VNA1.5, 3.0 = 0.999 σ CM + 0.0023; R2 = 0.999) was also observed between the σ measured using a conductivity meter (CM) and that estimated with the VNAs. Finally, a good correlation was also observed between θ measured in the field experiment with TDR100 and the VNA1.5 and VNA3.0 devices. [ABSTRACT FROM AUTHOR]

• Pedodiversity can increase soil retention services, but decreases water yield services. • Pedodiversity can increase the stability of soil retention services over time. • Environmental factors have both direct and indirect effects on ecosystem services. • Total effect of pedodiversity and environmental factor on ecosystem service is similar. Pedodiversity has an important influence on soil water movement, sediment transport, plant growth, biodiversity maintenance, and many other ecological processes related to ecosystem services. However, the influence of pedodiversity on ecosystem services is still unknown, especially in mountainous areas. In this study, the relationships between the pedodiversity and two essential ecosystem services, soil retention (SR) and water yield (WY) services, were analyzed, and the influences of pedodiversity on the temporal changes in the SR (DSR) and WY (DWY) during 2000 and 2015 were determined. The results showed that pedodiversity was generally positively correlated with the SR, but it was negatively correlated with the WY. This indicates that a higher pedodiversity is favorable to soil and water conservation. Both the SR and WY decreased during the study period. The Shannon index was significantly negatively correlated with the DSR, indicating that pedodiversity was conducive to maintaining the temporal stability of the SR. However, a positive correlation was found between pedodiversity and the DWY, indicating that the higher pedodiversity area exhibited a more significant decreasing trend in the WY. This in turn suggests that pedodiversity helps improve the water retention capacity. The influence of pedodiversity on ecosystem services is mainly a direct effect. However, the influences of the environmental factors had both direct and indirect effects. The results of this quantitative analysis of the influence of pedodiversity on ecosystem services provide evidence that protecting pedodiversity is necessary, and they also provide a new direction for pedodiversity research. [ABSTRACT FROM AUTHOR]

• A method measured soil matrix infiltration (SMI) by double-ring was improved. • The SMI of eucalyptus plantations decreased with increasing forest age. • Soil properties changing with forest age inhibited SMI in eucalyptus plantations. • Soil texture dominates the SMI of differently aged eucalyptus plantations. In this study, we improved the method for measuring soil matrix infiltration by using a surface-positioned double-ring infiltrometer. The soil matrix infiltration processes of four differently aged (1, 3, 5, and 7 years) eucalyptus plantations were measured in situ in a southern subtropical area in China. Soil matrix infiltration characteristics (SMICs), including initial infiltration rate (IIR), stable infiltration rate (SIR), and cumulative infiltration (CI), were calculated using the experimental data of the soil matrix infiltration process. The physical and chemical properties of layered soil (0–60 cm with an interval of 20 cm), including soil textures, buck density (BD), soil organic matter (SOM), and soil water stable macroaggregate (WSMA) closely related to infiltration, were analyzed. Results showed that the IIR (140.33–233.14 mm h−1), SIR (116.24–194.04 mm h−1), and CI (118.42–217.20 mm) decreased with increasing forest age. In addition, the SIR and CI of the 1-year-old eucalyptus plantation were significantly higher than those of the other plantations. The decrease trend of SMICs with forest age was attributed to the soil properties changing in the eucalyptus plantations. The clay content, BD, SOM, and WSMA increased and sand content decreased with increasing forest age, thus inhibiting the SMICs. The results of stepwise regression analysis showed that the sand content of topsoil (0–20 cm) was the main factor affecting IIR, and the clay content of deep subsoil (40–60 cm) was the dominant factor affecting SIR and CI. The in situ soil matrix infiltration measurement in eucalyptus plantations was achieved with the improved method, and the main influencing factors were clarified. The results enhance understanding of soil matrix infiltration and its effect on precipitation redistribution and are helpful in quantifying the water storage capacity of plantation soil. [ABSTRACT FROM AUTHOR]

• Surface soil moisture was mapped by using remote sensing data through machine learning. • Stacking reduced overfitting and individual model biases. • Backscatter coefficient, modified-NDWI and LST were most significant covariates in mapping. • High and low irrigation zones were identified from soil moisture maps. Soil moisture information is key to irrigation water management, drought monitoring, and yield prediction. It plays a vital role in the water cycle and energy budget between the earth's surface and atmosphere. Hence, its monitoring is crucial for both natural and anthropogenic environments. While the current remote sensing-based global SM products available at coarser resolution (3/15 km) are unsuitable for field-level operations, the most widely used microwave remote sensing suffers from model complexities and in-situ data requirements. Weather conditions limit the alternate approaches such as optical/thermal. This study aims to map surface soil moisture (SSM) at 30 m spatial resolution in a semi-arid region by fusing optical, thermal, and microwave remote sensing data using bagging, boosting, and stacking machine learning approaches. The reference data were collected using a soil moisture meter. The covariates included radar backscatter from Sentinel-1, visible, near-infrared, short-wave infrared, land surface temperature, and spectral indices derived from Landsat 8. Boruta algorithm was used for feature selection which identified radar backscatter, modified normalized difference water index, and land surface temperature as the most critical covariates impacting the SSM. The random forest (RF) showed the highest correlation coefficient (r = 0.71), and least root mean square error (RMSE = 5.17%). The cubist model had the least mean bias error (MBE = 0.21%) during independent validation. Stacking of cubist, gradient boosting machine (GBM), and RF using elastic net (ELNET) as meta -learner further reduced the MBE (0.18%) and RMSE (5.03%) during the validation. Overall, stacking multiple machine learning models improved model prediction and can be recommended to improve the digital soil moisture mapping. [ABSTRACT FROM AUTHOR]

• Ephemeral springs fed by perched aquifers identifiable only when discharge occurs. • Ecohydrogeological approach to detect them when no discharge occurs. • The grass Molinia arundinacea as an indicator of dry springs on ophiolites. • Area, cover and functional traits of Molinia related to the hydrologic gradient. Springs represent relevant habitats which support high levels of biodiversity and productivity, providing refugia to both plants and animals together with essential ecosystem services. However, springs are often overlooked or even destroyed by human activity. Locating, inventorying, and monitoring springs is, therefore, becoming of increasing importance. This study aims at developing a multidisciplinary approach to detect ephemeral springs, which can only be discovered by hydrogeological surveys when discharge occurs. We suggest potential cooperation between hydrogeologists and botanists based on the use of a plant species as an indicator of the occurrence of ephemeral springs fed by ophiolitic perched groundwater aquifers. In this study, the grass Molinia arundinacea was used as a bioindicator, observed in periods when there was no discharge and whose occurrence on ophiolite bodies was revealed by previous studies in the northern Apennines (Italy). A total of twenty ophiolitic bodies were explored and grassland stands including Molinia populations were discovered in 86 springs (15 reported for the first time). Detailed geomorphological and hydrogeological sampling was also performed in ten springs, recording the occupancy area, cover and functional traits of Molinia at two permanent and eight ephemeral springs and along their streambeds. Molinia not only colonised the spring outlets, but also occurred along the streambeds fed by ephemeral springs, with a higher occupancy area where the rocky outcrops were covered by detrital deposits and at the base of the morphological incision. Additionally, the cover of Molina populations was correlated with the average water discharge, with the highest functional trait values found in locations with high soil moisture. Results confirmed that while Molinia performs best on permanently moist soils, it is also able to grow on soils with a fluctuating water-table or even in dry conditions, thus representing an excellent indicator of springs fed by temporary perched aquifers. [ABSTRACT FROM AUTHOR]

• Soil water absorption and consumption were quantified in rubber agroforestry. • Intercropping increased topsoil water consumption but decreased the middle layer. • Intercropping supplemented soil water consumption through absorption. • Several ecosystem services correlated with soil water were improved. • Intercropping Alpinia oxyphylla with rubber realizes multi-win goals. Intercropping in plantations may alter soil water consumption, absorption and retention. However, little is known about how soil water changes impact ecosystem services. In the present study, we planted Alpinia oxyphylla Miq. (a medicinal herb) in rubber (Hevea brasiliensis) plantations and monitored daily soil water content in the surface (0–20 cm), middle (20–40 cm), and deep (40–60 cm) soil layers after intercropping. We analyzed the impact of soil water connected with ecosystem properties such as hydraulic conductivity, soil organic matter, root length density, and canopy density on water regulation, soil retention, soil fertility (available N, P, and K), and biodiversity (bacterial and eukaryotic diversity). Our results showed that intercropping significantly increased and decreased soil water consumption by 54.34% and 36.78% in the surface and middle soil layers, respectively. Water absorption increased by 52.93% and decreased by 39.58% in the surface and middle soil layers, respectively. Hence, water was replenished, and the water balance was maintained across soil layers. Moreover, soil water absorption rather than consumption, with hydraulic conductivity and root length density, predicted increases in water regulation and soil retention. Soil water retention positively promoted soil bacterial diversity, which could increase available P content in the surface soil layer. Our results confirmed that intercropping balanced soil water distribution and improved several ecosystem services without increasing water consumption across the entire system. Hence, intercropping does not exacerbate the water deficit. We propose that adaptive and profitable intercropping in rubber plantation should protects crop production and ecosystem services while promoting sustainable land use. [ABSTRACT FROM AUTHOR]

The shrub patch pattern has important influence on the ecosystems in the arid water-wind erosion crisscross regions. The objective of this study was to examine the effects of vegetation pattern of shrub spot patch on species diversity and soil water content at the sand in slopes in water-wind erosion crisscross region on the Loess Plateau. In this study, the shrub patch size was classified to four size classes, contrasting with bare land patch, and herbaceous plants, and soil water content of the shrub patch were measured in each patch. The Shannon–Wiener indices were 0.364 and 1.074 respectively in small and large patches, which were higher than 0.231 in the bare land patch. The Richness index was 1.41 in bare land patch, which was lower than 1.704 in small shrub patch and 4.370 in large shrub patch. The above- and below-ground biomass and surface soil water content were also significantly ( p < 0.05) higher in the shrub patch than that in the bare land patch. These results suggest that the shrub patch could significantly increased species diversity, the above- and below-ground biomass, and surface soil water content. Based on these results, the soil was aggregated in shrub patch and the vegetation pattern was successive and each cycle of vegetation pattern was benefited by its previous stage in the water-wind erosion crisscross region on the Loess Plateau. [ABSTRACT FROM AUTHOR]

Decreases in the water retention function of various artificial disturbed landform units (DLUs) caused by urbanization activities, compared to original landform units (OLUs), are the main factor that causes urban water and soil loss and the aggravation of urban floods under certain rainfall conditions and specially designed drainage network capabilities. Field investigations, laboratorial analyses of soil physical properties and analytic hierarchy process (AHP) composite methods were performed to comprehensively analyse the effects of various DLUs on the water retention function of OLUs. The results indicated as the following: (і) The > 5 mm particle content (> 54%) for various DLUs was higher than that for OLUs (lower than 3%); the natural repose angles of soil-rock mixtures (32–37°) and soil bulk density (1.41–1.74 g/cm 3 ) in the DLUs were all higher than those in the OLUs (30–31°, 1.18–1.14 g/cm 3 ); and the uniformity coefficients and curvature coefficients were 10.00–80.00 and 3.24–5.70 in the DLUs and 6.00–75.00 and 0.17–2.50 in the OLUs, respectively. (ii) The soil steady state infiltration rate in the DLUs decreased from disturbed soil accumulation with 2 months (DSA 2m , 15.00 mm/min) to disturbed soil accumulation with 2 years (DSA 2a , 5.63 mm/min), disturbed soil accumulation with 4 years (DSA 4a , 3.82 mm/min), the slope greening belt (SGB, 1.24 mm/min), and construction roads (CR, 0.51 mm/min). The conversion from forests to DSA 2m had the greatest impact on the soil infiltration capacity and soil storage capacity, while the conversion to CR had the lowest impact. (iii) The total reservoir storage in the DLUs' soil was ordered as follows: DSA 4a > SGB > DSA 2a > DSA 2m > CR. The conversion process from grass to CR exerted the greatest impact on storing water and regulating the overland flow. (iv) The water retention functions in the DLUs were all weaker than those in the OLUs: DSA 2m was the weakest (0.287), while paddy fields were the strongest (0.668). Thus, the occupied areas of urban water surfaces (e.g., lakes, rivers and ponds), forests and grassland and their spatial distribution during urbanization must be carefully considered. These results could help to understand the ecological service functions of urban soil and water conservation, provide relevant knowledge to landscape rehabilitation, alleviate urban floods during urban development and recover the functions of soil and water conservation ecological services in project areas during the urbanization construction process. [ABSTRACT FROM AUTHOR]

In this study eight temperate grassland sites were monitored for soil CO 2 efflux (R s ) and the spatial covariate soil water content (SWC) and soil temperature (T s ) at fine scale in over 77 measurement campaigns. The goals of this multisite study were to explore the correlations between environmental gradients and spatial patterns of R s , SWC and T s , which are not site-specific and to quantify the relevance of biotic and abiotic controls over spatial patterns along increasing vegetation structural complexity. These patterns in water-limited ecosystems in East-Central Europe are likely to be influenced by summer droughts caused by the changing climate. A consistent experimental setup was applied at the study sites including 75 sampling locations along 15 m circular transects. Spatial data processing was mainly based on variography. Two proxy variables were introduced to relate the site characteristics in terms of soils, water status and vegetation. Normalised SWC (SWCn) reconciled site-specific soil water regimes while normalised day of year integrated temperature and vegetation phenology. A principal component analysis revealed that the progressing closure of vegetation in combination with large R s and SWCn values, as well as low T s and R s variability support the detectability of spatial patterns found in both the abiotic and biotic variables. Our results showed that apart from SWC the pattern of soil temperature also had an effect on spatial structures. We detected that when the spatially structured variability of T s was low, a strong negative correlation existed between SWCn and the spatial autocorrelation length of R s with r = 0.66 (p < 0.001). However, for high spatially structured variability of T s , occurring presumably at low T s in spring and autumn, the correlation did not exist and it was difficult to quantify the spatial autocorrelation of R s . Our results are indicative of a potential shift from homogeneity and dominance of biotic processes to an increased heterogeneity and abiotic regulation in drought prone ecosystems under conditions of decreasing soil moisture. [ABSTRACT FROM AUTHOR]

Soil microbial communities play an important role in regulating land–atmosphere CO 2 exchange in terrestrial ecosystems. However, their responses to climate change are unclear. We explored the effects of water and nitrogen addition and their interaction on soil microbes and the resulting impacts on soil carbon emissions in the Gurbantunggut Desert, northwestern China. A manipulative 30% increase in precipitation and 5 gN m − 2 year − 1 deposition alone and in combination was applied across three years from 2011 to 2013. Water addition significantly increased microbial biomass and respiration, metabolic quotient, and the utilization of carbohydrates, carboxylic acids and amino acids. Water addition did not change the microbial community composition. Nitrogen addition only significantly increased soil bacterial PLFAs, while exerting no significant impacts on soil fungal PLFAs, microbial respiration and soil respiration. Moreover, nitrogen addition had no significant impacts on microbial community composition. Water and nitrogen addition in combination did not generate synergistic effects on microbial communities and soil respiration. Across treatments in three years, soil respiration and microbial respiration were positively correlated with microbial total PLFAs, microbial carbon utilization profiles, while being independent of microbial community structure. This study suggests water addition can increase soil carbon emission through increasing microbial utilization of labile carbon, and water plus nitrogen addition had no synergistic effects on soil microbial communities and soil respiration, demonstrating nitrogen is not a limiting factor for soil microbial communities in the scenario of increasing precipitation in this desert ecosystem. [ABSTRACT FROM AUTHOR]

The objective of this study was to explore the correlations between Tamarix and soil water salinity parameters and groundwater depth under saline mineralization conditions and to reveal the transport rules and exchange effects of salinity in soil- Tamarix systems with different groundwater depths. Soil columns planted with Tamarix chinensis ( T. -soil column) grown in the Yellow River Delta were chosen for modeling. Six different groundwater depths were simulated in the models. We measured and analyzed the water and salinity contents of different soil profiles with different groundwater levels and Na + contents in new T. chinensis branches and leaves. The results showed the following: (1) under shallow and medium groundwater levels, with increasing soil depth, the differences in the water contents between the T.- soil column and the control soil layer gradually decreased. Under deep groundwater levels, the differences increased and then decreased. Planting T. chinensis decreased the soil water content, and higher groundwater levels corresponded with a greater decrease in the soil water content of the T.- soil column. With increasing groundwater depth, the depth at which the water content of the T.- soil column suddenly changed increased. When the groundwater levels were 0.6 m, 0.9 m, 1.2 m, 1.5 m, and 1.8 m, the critical depths at which the water contents suddenly changed in the T.- soil columns and control were 0.3 m, 0.5 m, 0.7 m, 1.0 m, and 1.3 m, respectively. (2) Although planting T. chinensis clearly decreased soil salinity, the amplitude of the decrease increased and then decreased with increasing groundwater depth. The maximum decrease was reached at a groundwater level of 1.2 m. Importantly, the groundwater level of 1.2 m was the critical level for increasing the capillary water in the T.- soil column and was the depth at which the water and salinity significantly changed (the water and salinity turning depths). When the groundwater depths were 0.6, 0.9, 1.2, 1.5 and 1.8 m, the water turning depths in the T.- soil columns and control were 0.3, 0.5, 0.7, 0.7 and 0.7 m, respectively. Under medium (0.9 m and 1.2 m) and deep (1.5 m and 1.8 m) groundwater depths, the minimum soil salinities in the T.- soil column occurred at depths of 0.5 m, 0.7 m, 0.7 m, and 1.0 m, respectively. (3) With increasing groundwater depth, the water contents of the T.- soil column, T. chinensis leaves, and new branches gradually decreased. The salinity of the T. chinensis leaves decreased and then increased, and the salinities of the T.- soil column and new branches increased and then decreased. Under different groundwater depths, the water contents of the T. chinensis leaves were significantly higher than the water contents of the branches, and the salinity contents of the leaves were significantly lower than the salinity contents of the branches. With increasing groundwater depth, the water transported from the branches to leaves of T. chinensis significantly increased, and the ratio of Na + that migrated decreased and then increased. [ABSTRACT FROM AUTHOR]

Soil water erosion on cultivated lands represents a severe threat to soil resources in the world, and especially in Mediterranean areas, due to their topographic, edaphic and climatic conditions. Among the cultivated lands, vineyards deserve a particular attention because, aside representing one of the most important crops in terms of income and employment, they also have proven to be the form of agricultural use that causes one of the highest soil losses. Although the topic of soil water erosion on vineyards has been studied, it still raises uncertainties, due to the high variability of procedures for data acquisition, which consists into different scales of analysis and measurement methods. There is still a great gap in knowledge about the effect of triggering factors on soil water erosion and, so far, an effort to quantify this effect on the Mediterranean viticulture has not been made yet. Therefore, this paper review aims to (i) develop a documented database on splash, sheet and rill erosion rates in Mediterranean vineyards, (ii) identify and, if possible, quantify the effect of triggering factors such as topography, soil properties, rainfall characteristics and soil conservation techniques on soil water erosion, and (iii) provide suggestions for a more sustainable viticulture. Although the large variability of data, some general trends between erosion rates and triggering factors could be found, as long as data were categorized according to the same measurement method. However, no general rule upon which to consider one triggering factor always predominant over the others came out. This paper review supports the importance of monitoring soil water erosion by field measurements to better understand the relationship between the factors. However, protocols should be established for standardizing the procedure of collecting data and reporting results to enable data comparison among different study areas. [ABSTRACT FROM AUTHOR]

Surface and groundwaters of El Divisorio brook (Argentina) have excessive As (WHO, USEPA, CAA: > 10 μg L − 1 ). The rural population is at risk of arsenicism because groundwater is the only source of water for human consumption. We analyse geoavailability of As and other associated elements (Ba, Br, Co, Cr, Fe and Na) in the solid phase (INAA-Actlabs), determine the association between As and other elements in the mineral suite and in waters, quantify Fe oxides (Fe ox ; Mehra and Jackson) and interpret their relationship with As, total Fe (Fe total ) and Na in the solid phase applying Principal Components (PC) to understand factors and processes that rule their incorporation into groundwaters and to identify areas at risk of elevated As in waters. Intrabasin variability of total As content (range 5.80–20.70 mg kg − 1 ) with the highest amounts towards the discharge areas and a more irregular vertical distribution, particularly in the alluvial plain, reflects differences in As-bearer frequencies. Arsenic is slightly lower in the Bw horizons compared with the A and C horizons and it increases in the Bt horizon through clay illuviation. More than 90% of sodium-bicarbonated surface and groundwaters showed As > 10 μg L − 1 (range: 10 to 114 μg L − 1 ) with the highest levels in the middle–lower basin. The highest contributions to PC1 were Br (0.673), Co (0.868) and Na (− 0.769); As (0.814) and Cr (0.686) were relevant to PC2 and Ba (0.501) and Fe (0.783) were relevant to PC3. In the upper basin, a greater amount of Na withheld in the solids promotes a less aggressive geochemical environment and prevents As from entering waters, thus yielding lower As levels in the aquifer compared with the middle–lower basin. Here, alkalinity (pH: 7 up to > 9) promotes weathering and liberation of As from volcanic glass and other carriers, formation of As oxyanion species together with As desorption from charged clays and Al–Fe–Mn sesquioxides and concentration up to unacceptable levels in solution. Landform configuration, climate and pedoclimate, the residence time of water and the local hydrogeochemical variables (pH, competition with other ions, adsorption–desorption) control mobility and concentration of As in a dynamic equilibrium with the local chemistry. Evaporation (subhumid to semiarid climate) and oxyion competition reinforce As accumulation in the shallow aquifers. [ABSTRACT FROM AUTHOR]

Dynamics of large wood in aquatic systems significantly influence physical and ecological processes in rivers. Wood mobility is notably becoming a critical issue, not only in the context of restoration, but also in terms of flooding and hazard potential. Although the number of studies focusing on instream wood has increased substantially over the last few years, physical properties of wood have rarely been measured in aquatic systems. Instead, forest industry-based standards are often used. In this study, we quantitatively assess properties of instream wood density using decayed samples from the Rhône River stored within the Génissiat Reservoir and green samples from the Ain River floodplain (France). Using in-situ and laboratory experiments, we demonstrate how wood density varies between species, how density changes with moisture sorption and decay, and how density affects buoyancy. Results illustrate that both green (e.g., 800 ± 170 kg·m − 3 ) and instream woods (e.g., 660 ± 200 kg·m − 3 ) have much greater densities than standard values used in the literature (500 kg·m − 3 ). Sorption processes differ in green versus instream wood; moisture desorption of green wood is faster than absorption, whereas for instream wood, absorption is faster than desorption. These findings and the related changes in density affect wood buoyancy and mobility and therefore influence wood dynamics in rivers. Finally, two case studies illustrate how more accurate density values can be used to improve wood transport modeling and wood budget estimates based on numerical simulation and ground video-imagery-based monitoring. [ABSTRACT FROM AUTHOR]

In the semi-arid Horqin Sandy Land of northern China, Caragana microphylla , a leguminous shrub, is the dominant plant species widely used in re-vegetation efforts aimed at stabilization of mobile sandy lands. However, the effect of rainfall characteristics on soil water dynamics and deep percolation in C. microphylla shrublands are not well understood. The objective of this study was to examine the responses of volumetric water content (VWC) and deep percolation under the root zone of C. microphylla to different rainfall characteristics. An underground chamber with 23 concrete basins (200 × 200 × 230 cm 3 ) was constructed to conduct this experiment during the growing seasons from 2010 to 2013. For this study, three of the basins were filled with sandy soil taken from the C. microphylla shrublands near to the station (about 200 m) and one C. microphylla shrub was transplanted into each basin in 2009. The corresponding hourly rainfall data were obtained from an automated meteorological station. VWC was recorded hourly using MiniTrase Soil Moisture Monitoring System at 0–20, 20–40, 40–60, 60–80, 80–100, 100–120, 120–140, and 140–160 cm soil depths. Deep percolating water was collected in the underground chamber and measured daily. Our results showed that rainfall amount, intensity, duration, and the duration of the dry interval were significantly correlated with VWC in different soil layers. The amount of deep percolation was significantly correlated with rainfall amounts and rainfall duration, but not with rainfall intensity and the duration of the dry interval. Average deep percolation in C. microphylla shrublands was 97.5, 114.3, 66.8, and 15.1 mm in 2010, 2011, 2012, and 2013, respectively, and accounted for 62.79%, 49.41%, 27.96%, and 7.36% of rainfall during the growing season. The coefficient of deep percolation was significantly negatively associated with annual mean shrub cover and canopy size, but not with annual mean height of C. microphylla . Our results suggested that re-vegetation with C. microphylla in this region is likely to result in a reduction in potential groundwater recharge and decrease of soil water content relations with an increase in age of the shrub. [ABSTRACT FROM AUTHOR]

Wetting–drying (W–D) cycles can cause significant modifications on soil hydro-mechanical behavior. In this investigation, both initially saturated slurry specimens and unsaturated compacted specimens were prepared and subjected to three W–D cycles. The temporal–spatial evolution of soil profile mechanical behavior during each drying path was characterized by penetration test using a micro-penetrometer. The results show that the employed micro-penetrometer provides a simple, quick and reliable tool to evaluate soil profile mechanical behavior. As initially saturated soil is subjected to drying, the overall profile penetration resistance changes slightly before a critical water content is reached. After that, it increases quickly with decreasing water content. The drying induced improvement of soil mechanical behavior exhibits evident delayed effect in profile. The effect of W–D cycles on soil profile mechanical behavior depends on soil initial state. For initially saturated slurry specimens, the overall profile penetration resistance generally decreases with increasing W–D cycles, and the reduction between the 1st and 2nd drying paths is much higher than that between the 2nd and 3rd drying paths. While for initial unsaturated compacted specimens, the overall profile penetration resistance during the 1st drying path is lowest, and reaches the maximum value during the 2nd drying path. It is also found that, whatever the initial state, profile structure defects are created after the specimens are subjected to the 3rd W–D cycle. During the 3rd drying path, the penetration resistance shows evident fluctuation in profile, and this phenomenon is more pronounced at relatively low water content condition. [ABSTRACT FROM AUTHOR]

Aims Antecedent soil water content (ASWC) is an important factor affecting soil water infiltration, runoff and soil erosion on slopes but it is difficult to measure or forecast accurately and is not often reported in soil erosion databases. Methods Runoff plots (12 m × 5 m) were used to collect runoff and sediment during the rainy seasons between April 2010 and October 2013 on the Loess Plateau, China. The HYDRUS-1D model was calibrated and tested using the data collected from the plots. The relationships of ASWC with runoff and sediment yield were investigated using the model output values for ASWC. Results The model performance was satisfactory, with a mean Nash–Sutcliffe model efficiency coefficient of 0.411 and a root mean square error of 0.031 during the four study years. Runoff was directly affected by rainfall amount and rain intensity. Furthermore, runoff typically increased with ASWC. Conclusions HYDRUS-1D can provide temporal ASWC data that could be used for runoff prediction. [ABSTRACT FROM AUTHOR]