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[Display omitted] • Soil silt/clay and nutrients increased with increasing distance from the shelterbelt. • Downslope deposition lead to an increase in plow pan thickness and a decrease in bulk density. • Erosion rate was primarily affected by shelterbelt distance, followed by elevation. • Sites closer to shelterbelt warrant particular attention due to coarse-texture materials. Soil erosion is the most severe form of land degradation globally. Farmland shelterbelts are important for reducing erosion, especially erosion caused by the co-occurrence of water and wind. However, few studies have focused on how the distance from the shelterbelt associated with farmland topography affects the redistribution of soil quality indicators. The aims of this study is to reveal the relative importance of these two factors to soil quality under typical wind and water erosion conditions concurrent with the Songnen Plain, China. Topsoils (0–10 cm) were sampled at seven distances from the shelterbelt with three replicates, where topography heterogeneity was also considered. We found that the silt/clay content and soil nutrients at sites farther from the shelterbelt were significantly greater than those at sites closer to the shelterbelt (P < 0.05). Similarly, deposition was dominant at sites farther from the shelterbelt and downslope positions, while erosion was dominant at sites closer to the shelterbelt and upslope positions. Moreover, we discovered that the relative influence of distance from the shelterbelt and farmland elevation varied with individual soil quality indicators. Soil nutrients increased through the deposition of more fine-textured soil (silt/clay) positions farther from the shelterbelt. The downslope region responds to soil deposition by enhancing the plough pan thickness and lowering the bulk density and pH. Overall, distance from the shelterbelt and farmland elevation had interactive effects on soil quality, and erosion was primarily affected by distance from the shelterbelt (63.4 %), followed by elevation (22.7 %). Furthermore, the sites closer to the shelterbelt (i.e., 20 to 420 m) warrant particular attention due to the deposition of coarse-texture materials here. This work is crucial for an improved understanding of the synergistic effects of long-term water and wind co-occurrence on soil quality evolution. [ABSTRACT FROM AUTHOR]

• Patchiness caused significant reduction of SOC and TN stocks. • Reduced vegetation input and increased erosion output accounted for SOC and TN loss. • Grasslands with high patchiness had a great potential for C and N sequestration. Patchiness acts as an indicator of terrestrial ecosystem degradation and can lead to considerable loss of soil organic carbon and total nitrogen. However, quantitative assessments of the effects of patchiness on soil organic carbon and total nitrogen stocks and their associated mechanisms remain limited. This study aimed to explore the influence mechanisms of patchiness on soil organic carbon and total nitrogen stocks and to project the quantitative contribution of the further expansion of patchiness and vegetation recovery. Soil properties, soil organic carbon and total nitrogen stocks were investigated using a combination of field sampling and aerial photography in four grassland types, alpine meadow, alpine steppe, temperate grassland, and desert grassland, at 47 sites in northwestern China. Soil organic carbon and total nitrogen densities in the bare patches were 34–54 % and 23–41 % lower, respectively, compared to the original vegetation. At the plot-scale, current soil organic carbon and total nitrogen stocks ranged from 30.85 to 77.80 T/ha and 3.26 to 10.19 T/ha, respectively, across grassland types; with a 10–27 % and 7–24 % potential loss of soil organic carbon and total nitrogen stocks, respectively, from the further expansion of patchiness but a 10–50 % and 9–37 % potential increase in soil organic carbon and total nitrogen stocks, respectively, from vegetation recovery. Soil organic carbon and total nitrogen stocks were positively correlated with vegetation biomass, soil clay content, and precipitation (p < 0.001), whereas they were negatively correlated with patchiness (p < 0.001). In summary, patchiness reduced soil organic carbon and total nitrogen stocks by decreasing vegetation inputs and increasing erosion outputs, while vegetation recovery showed potential for increasing carbon and nitrogen stocks. Our results highlight that maintaining intact vegetation cover is critical for preserving terrestrial ecosystem carbon and nitrogen storage. [ABSTRACT FROM AUTHOR]

[Display omitted] • Invasion by Spartina increased mineral-bound OC in mudflat soil. • Subsequently reclamation for aquaculture decreased soil mineral-bound OC. • Mineral-bound OC was correlated to nitrogen supply and soil clay content. • Habitat change affected Fe[Al]–OC more than Ca-OC and residual-OC. • Soil OC storage increased more strongly with increasing Ca-OC. The formation of mineral-bound organic carbon (OC) complexes is important for the long-term preservation of soil organic carbon (SOC) in wetlands. Many coastal wetlands globally have been threatened by plant invasion and land development, but information on the effects on mineral-bound OC is limited. We measured the soil contents of Ca-OC, Fe(Al)–OC and residual OC across 21 coastal wetlands in southern China that have gone through the same sequence of land cover change, from native mudflats (MFs) to Spartina alterniflora marshes (SAs) then to earthen aquaculture ponds (APs). Residual-OC was the main component of SOC (74.1–78.2 %), followed by Fe(Al)–OC (18.4–22.8 %) and Ca-OC (<3.5 %). All three components in the soil increased when MFs were converted to SAs, but decreased in subsequent conversion of SAs to APs. Land cover change affected Fe(Al)–OC the most, but SOC storage increased more strongly with increasing Ca-OC. Nitrogen supply in the form of NH 4 +-N and clay content both positively affected the changes in mineral-bound OC. Our results suggest that different land cover change scenarios had different effects on the amounts of mineral-bound OC and their liability to microbial turnover, resulting in different degrees of SOC preservation and carbon emissions. [ABSTRACT FROM AUTHOR]

[Display omitted] • Suitable plantations can mitigate global change events, if well-implemented. • China's plantations show increasing above- and below-ground carbon stocks with stand age. • C stocks and rates increase with temperature as compared to humidity. • Soil clay and fertility increase C stocks rather than annualized C rates. • C allocation between tree organs depends on climate and soil conditions. A significant proportion of the Earth's natural forests has been continuously degraded each year as a result of human activities and global environmental changes. Meanwhile, there has been a rise in the establishment of plantations through numerous planting trees initiatives, including those recently spearheaded by the United Nations (UN) Decade (2021–2030). Yet, considerable global uncertainty remains on drivers of carbon (C) sequestration (defined by C stocks and annualized accumulation rates) in plantations. By using the meta -data from 257 plantation plots in China, we quantified above- and below-ground C stocks and annualized C accumulation rates in tree organs, i.e., stems, branches, leaves, and roots, based on biomass allometric equations and scaling rules. Multiple linear regression models were used to explore the drivers (i.e., stand age, climate and soil factors) of plantation above- and below-ground C stocks and accumulation rates. We show that above- and below-ground C stocks increased with stand age (β = 0.55 to 0.66; P < 0.001) followed by temperature (β = 0.29 to 0.36; P = 0.001 to < 0.001), precipitation seasonality (β = 0.23 to 0.41; P = 0.013 to < 0.001), and somehow by climatic humidity (β = 0.17 to 0.35; P = 0.105 to 0.002), but decreased with isothermality (β = -0.14 to -0.16; P = 0.024 to 0.019). Soil clay content increased stem C stock (β = 0.15; P = 0.016) whereas soil cation exchange capacity increased branch C stock (β = 0.23; P = 0.003), even though soil factors did not significantly affect annualized C accumulation rates (β = -0.12 to 0.14; P = 0.908 to 0.078). This coarse-scale study suggests that C sequestration in China's plantations increases over time with increasing climatic temperature and soil fertility, thereby sustaining environmental conditions by capturing C from the atmosphere and storing it in tree organs. Thus, conserving environment-friendly plantations, having no disruption to native biodiversity, as land resources can reduce pressures on natural forest resources while improving environmental integrity through feedback. [ABSTRACT FROM AUTHOR]

• Regional geochemical baseline values can well model the background values of studied metals. • Cd was the main pollutant in the riparian sediment. • The contamination and risk of Cd was high in upper downstream and site of 24. • Influencing factors explained variation of metals better at 1 km buffer scale. • Land use composition contributed most to the high explanation at 1 km scale. In this study, we assessed pollution status and potential risk of metals in riparian sediment of Yangtze River with geo-accumulation index (I geo), ecological risk index (RI) and health risk index (THQ) by calculated regional geochemical baseline (RGB) values. We explored the influence of natural factor (sediment property) and anthropogenic factors (land use composition and landscape configuration) at different buffers (500 m, 1 km and 5 km) on metals in sediment using redundancy analysis (RDA) and variation partitioning analysis (VPA). Results indicated that RGB values can effectively model background values of metals (p < 0.01). I geo and RI assessment showed that Cd was the primary pollutant, which showed no contamination to moderate contamination (I geo > 0) and moderate ecological risk (ecological risk factor > 40) in upper downstream of the river. Besides, Cd showed moderate to strong contamination (I geo > 2) and considerable ecological risk (ecological risk factor > 160) at site 24, which is located in the intersection of Poyang Lake and Yangtze River and strongly affected by natural erosion and human activities of Poyang Lake drainage. THQ assessment indicated low health risk of metals from consuming fish influenced by suspended sediment. RDA and VPA analysis indicated that explanation rate of land use composition, sediment property and landscape configuration on metals was 27.01–55.1 %, 36.66 %, 9.77 %-12.52 %, respectively. The total explanation rate was significantly higher at 1 km scale (82.5 %), which was mainly contributed by land use composition and its interaction with sediment property and landscape configuration (55.11 %). Specifically, percentage of farmland, grassland, wetland and forest, content of TN, TOC, silt and clay in soil and landscape configuration index of NumP were positively correlated with metals, and content of sand in soil and landscape index of MSI negatively correlated with metals in riparian sediment at different buffer scales. Our results offer valuable insights for safeguarding riparian zone. [ABSTRACT FROM AUTHOR]

• The response of soil water content (θg) to vegetation restoration mode varied highly. • θg increased with soil depth and the distance from the ephemeral gully (EG) head. • θg was less on EG top with artificial plant than on EG top with natural plant. • Natural succession is recommended to control soil erosion and maintain soil water. Vegetation restoration in an ephemeral gully (EG) can alter the traits of soil, vegetation, and microtopography, and therefore likely influences soil water. Nevertheless, few results have been reported regarding the response of soil water regime to vegetation restoration modes in EGs in semiarid region. This research was designed to clarify the spatial variation in soil water in an EG with different restoration modes on the Loess Plateau of China. For the selected EG, the two banks of ephemeral gully were well restored by natural succession and artificial planting. Soil water content (θg) was quantified on the ephemeral gully floor (F), natural successional restored ephemeral gully top (NT), and artificial planted restored ephemeral gully top (AT) in both the vertical and longitudinal directions. A sloping farmland was selected as the control. The results revealed that θg increased significantly with soil depth (i.e., 0–1 m) and the distance from the ephemeral gully head (i.e., 0–60 m). In the vertical direction, the mean θg of the six test points of the ephemeral gully floor was 1.1 to 1.2 times greater than that of the control in each soil layer, while the mean θg of the six test points of NT and AT decreased by 12.3 % to 15.6 % and 29.2 % to 29.9 % compared to the control in each soil layer. Along the longitudinal direction, the θg (i.e., 0–1 m soil layer) abided by the pattern of F > NT > AT. The difference in θg between the three ephemeral gully units and their variations in the vertical and longitudinal directions were mainly driven by the variations in soil clay content, bulk density, organic matter content, plant root density, plant litter density, and the distance from the ephemeral gully head. The findings are useful to clarify the spatial variation in soil water and to select a reasonable vegetation restoration mode on hillslopes in semiarid regions. [ABSTRACT FROM AUTHOR]

Soil pore structure over a wide range of pore sizes regulates soil functions and relies heavily on pedogenic processes. To date, limited knowledge is available on the spatial variations of soil pore structure and underlying mechanisms over a broad geographic scale. Herein, seven typical zonal soils with increased status of soil development in heavy-textures were collected at different genetic horizons under forests along the mid-temperate to tropic climate gradient in eastern China. Pore size distribution (PSD, 0.006 ∼ 800 μm) of aggregates (sized ∼ 1 cm3) and other pore structure characteristics (void ratio, pore area and average diameter) were determined by mercury intrusion porosimetry. Differential PSD displayed tri- or bi-modal patterns and different pore size classes followed diverse geographic trends. Textural pores most influenced by soil type exhibited larger void ratio and pore area in highly than in moderately developed soils; structural porosity most influenced by soil horizon overall decreased with increased soil depth, indicating the decreased levels of hierarchical aggregation whatever soil type. Relative to soil texture and total organic matter (0.70≤|r|≤0.92), total and textural pores were more related to inorganic cementing agents (0.71≤|r|≤0.95, p < 0.001), where kaolinite and free iron/aluminum oxides (mainly crystalline form) exerted the positive effects on void ratio and pore area through clayey pores, in contrast to vermiculite and exchangeable cations; void ratio and pore size of structural pores could be separately promoted by sand-silt size organic matter and vermiculite (r = 0.79 and 0.73, p < 0.001). Additionally, clay-sized organic matter, sand, and free manganese oxides played a secondary effect (R2 = 0.04 ∼ 0.30, p < 0.05) and their specific roles differed with pore size class. The overall results suggest that the dramatic geographic variations of soil pore structure are controlled by both inorganic cementing agents and specific organic components to a large extent at the regional scale. [ABSTRACT FROM AUTHOR]

[Display omitted] • We studied the effects of moisture content, slope angle, and clay contents on mass failure. • A self-designed hollow model was used. • Indoor hollow-flume experiments were conducted under the condition of surface runoff. • Soils with 5%, 7.5%, and 10% initial water content generate fatal mass failure. • Soil mass failure occurs when critical water and clay contents are reached. Soil mass failure disasters are among the most destructive disasters in mountainous areas worldwide, and they continue to receive significant attention in the literature. However, factors that influence soil mass failure in hollows have not been explored via experimental approaches. In this study, we conducted a series of indoor hollow–flume experiments to exhibit how the three factors, namely, initial moisture content, slope angle, and clay content, influence the collapse of soil mass under surface runoff conditions. Our findings revealed that the major processes causing soil mass failure were internal seepage erosion resulting from subsurface runoff, migration of fine particles, development of tension cracks, increase in pore water pressure, and decrease in cohesion. Fluctuations in pore water pressure were characterized by two main trends: (1) an abrupt rise under static liquefaction and (2) a decrease before failure due to dilatancy. The time required for soil mass failure first decreased and then increased with the increase in moisture content. The soil mass with an initial moisture content of ∼12.5% was more critical to the failure. In addition, the time required for soil mass failure decreased with increasing slope angle, revealing a slope angle of 40° to be more prone to failure. The buildup of pore water pressure was found to increase with clay content; soil with a clay content of ∼7.5% required the shortest amount of time to initiate slides. Thus, our results provide a thorough insight into the processes and factors involved in the initiation and development of soil mass failure in hollow areas, which can be used by public agencies to improve monitoring, early warning, and forecasting systems. Notably, our study can help identify risk-prone source areas, and sensors can be installed to monitor potential mass failure locations. [ABSTRACT FROM AUTHOR]

• Rill morphology evolution on 4 coarse-textured topsoils is studied by laser scanning. • Rill headward and downward erosion are two mutually reinforcing processes. • Soil erosion intensity can be indirectly evaluated by geomorphologic comentropy. The sheet and rill erosion phases dominate the erosion process of the catchment area and up-slope of Benggang (a special gully) area, and its evolution has a vital impact on erosion characteristics in the erosion feedback loop. Here, the rill development processes, morphological characteristics and corresponding soil loss were investigated by laser scanning on the four coarse-textured granite topsoils defined as WH, TC, GX, and CT for the counties of Wuhua, Tongcheng, Ganxian, and Changting in China, respectively. A soil flume (3 × 0.8 m) at a slope gradient of 16.7% was treated with rainfall-inflow at the upslope inflow rate of 2 L min−1 and rainfall intensity of 90 mm h−1. Results showed that soil erosion rate increased with erosion evolution (sheet erosion, rill advance, and rill maturity phases). A comparison of the four different soils exhibited that the soil erosion rate showed a downtrend with the increase of soil clay and gravel contents. Specifically, the CT soil with high clay and gravel content showed the minimal soil erosion rate (0.024 kg m−2 min−1), rill density (0.95 m m−2), headward erosion rate (0.41 cm min−1), and surface evolution rate. The maximal soil erosion rate and rill depth were observed on the WH slope, with the rill headward erosion rate reaching the maximum of 20.59 cm min−1. Despite no significant difference in the geomorphologic comentropy of the four soils, their variation trend and rate could reflect dynamic changes in erosion. The total sediment transport efficiency was improved by rill formation and development, with rill erosion contributing to about 70% of total soil loss for the four soils. This study can enrich our understanding of the rill erosion process and surface morphology of coarse-textured topsoils. [ABSTRACT FROM AUTHOR]

• Mixed forests show a higher soil erosion control benefit than monocultures. • Tree-shrub mixtures reduce runoff and sediment more than tree-tree mixtures. • Mixed forests have the strongest positive impact on soil erosion control in dry areas. • Mixed forests are found to affect soil erosion most efficiently after 20 years of tree growth. • Mixed forests have the highest impact on soil erosion control on slopes of 16–20°. Soil erosion poses a major threat to the sustainability and stability of global terrestrial ecosystems. Mixed forests have more advantages in restoring degraded land and enhancing soil fertility than monocultures, but their influence on soil erosion remains uncertain. Therefore, we presented a meta -analysis consisting of 261 paired observations of mixed forests and the corresponding monocultures from 65 studies to evaluate the effect of tree diversity on soil erosion in China. The results showed that compared with monocultures, mixed forests significantly reduced the annual runoff and sediment yield by 17.4% and 23.6%, respectively. Tree-shrub mixtures showed more efficiency in reducing runoff (24.2%) and sediment yield (32.1%) than tree-tree mixtures. However, the positive effect of mixed forests on soil erosion control was significant > 20 years after stand establishment. Mixed forests showed the highest capacity to control soil erosion at slope angles of 16°-25° (runoff: 27.7%; sediment yield: 37.7%). In terms of soil textures, mixed forests performed better with respect to soil erosion control on sandy soils (runoff: 21.4%; sediment yield: 30.1%), whereas significant differences were not observed between different stand types on clayey soils. In addition, in the dry areas (humidity index (HI) < 30), mixed forests conferred the greatest benefits in reducing runoff and sediment yield (25.8% and 33.0%, respectively). Our results indicate that increasing tree species richness is a suitable approach to controlling soil erosion in China. This research provides a scientific basis for the management and sustainable development of forest ecosystems in the future. [ABSTRACT FROM AUTHOR]

[Display omitted] • Coarse-textured soil surface morphology evolution is studied by simulated rainfall. • Surface enriched coarse grains are quantified by photography and binarization. • Soil loss in inter-rill areas is controlled by surface coarse-grain coverage. • Soil clay content and stream power is shown to fit erosion prediction. The evolution of slope surface morphology directly affects the hydrological process and forms a dynamic feedback loop with the runoff and sediment production. However, the unique erosion processes and feedback mechanism for the surface morphological changes of coarse-textured granite soils have been rarely studied previously. Here, a series of rainfall simulation experiments (intensity of 90 mm h−1) were conducted under continual intermittent rainfall conditions (duration of 20 h) on a 0.8 m by 3.0 m soil flume packed with the four coarse-textured granite soils (sieved soils from the counties of Tongcheng, Ganxian, Changting, and Wuhua, China, defined as TCA, GXA, CTA and WHA, respectively) to measure the surface roughness, coarse grain coverage, soil erosion rate, stream power and sediment sorting. The results showed: 1) the coarse grain coverage of the four soils gradually increased with rainfall duration, with the final maximum (74.89%) for CTA soil, which corresponded to the enrichment of fine particles in the sediments; 2) the mean soil erosion rate of the four soils ranged from 0.090 to 0.76 kg m−2 min−1 with the decrease of clay content from 24.19% to 13.60% in the original soils, coinciding with the surface roughness controlled by rill erosion around the coarse grains; 3) the coarse grain cover provided a protective layer to reduce further soil loss in inter-rill areas; 4) the model of soil clay content and stream power was shown to be suitable for soil erosion prediction of coarse-textured soils (R2 = 0.93). The results highlighted soil mechanical composition and coarse grain coverage on the surface as the key factors affecting the coarse-textured soil erosion. This study facilitates our understanding of the unique erosion processes and the erosion feedback mechanism of coarse-textured soils. [ABSTRACT FROM AUTHOR]

Abstract: The collapse of overhanging layers of the heads and sidewalls of gullies accelerates gully development. Thus, the development features of the collapse of overhanging layers must be understood. In this study, the process of collapse of overhanging layers in man-made soil bodies containing different soil layers was investigated by flow scouring experiments. A soil body composed of a lower sandy layer and an upper layer of clay soil was evaluated, and a field soil profile was modelled in a test tank with an open side. The results revealed that the occurrence of the collapse of overhanging layers could be attributed to the development of a scour hole in the open side; the greater the flow rate, the lower the proportion of on-wall runoff. On-wall runoff played a more important role in the development of scour holes than off-wall runoff. The shape of scour holes formed under different flow conditions was similar. Also, the scour hole is not apparently related to the flow rate, implicating that the collapse is more dependent on rainfall (runoff) time rather than rainfall (runoff) intensity in the studied region; this is substantially different from other soil erosion types that are closely related to rainfall intensity. Moreover, the maximum length (SL ) and height (SH ) of the scour holes increased gradually with accumulated flow and scouring time; in addition, the height of the hanging soil body (HD ) gradually decreased, and a linear relationship between SL and HD was observed (HD =−0.359; SL +117.3; R 2 =0.861; P=0.003). After the seventh scour test, the scour hole triggered the collapse of the upper clay layer. The cantilever model was modified to predict the stability of the overhanging soil body. It provided a satisfactory explanation of the static balance of the weight of the soil as well as the tensile strength. After the seventh scour test, the measured and predicted threshold values of HD , SL , and TC were nearly equal, and a stable balance state was attained. However, when a 10cm tension crack appeared in the overhanging soil body, a stable balance state was obtained during the sixth scour test. [Copyright &y& Elsevier]

[Display omitted] • Weathering pedogenic process were main source of heavy metals in tea garden. • Organic matter and redox process control transfer of As, Pb, Cd and Hg. • Geochemical behaviors of Cr, Cu, Ni and Zn were related to pH and iron oxides. • Tea type, bedrock, soil texture and fertilizer affected metals transfer mainly. • High risk by Pb and Cd existed in area with granite/granodiorite and shale. As one of the most popular beverages around world, factors influencing transfer of heavy metals from soil to tea leaves is crucial to investigate and assess health risk through tea drinking. Parent material (PM), soil and tea samples from Anhui province, typical tea producing area in China were collected in this study. To find out distribution characteristics of heavy metals in tea and soil, and influencing factors for transfer process, variables of plantation factors, soil properties and geological background were taken into account. The results showed that weathering pedogenic process could be the main release source of heavy metals in soil under the acid environment for tea growth. More than 75% of soil Cd, Hg, Pb and Zn exceeded background. However heavy metals in tea samples were below the limits of China, WHO and EU standards. Soil organic matter and redox process influenced the distribution and transfer of As, Pb, Cd and Hg in soil and tea. While geochemical behaviours of Cr, Cu, Ni and Zn were mainly related to soil pH and iron oxides in tea garden. The method of classification and regression trees (CART) showed clones of tea type, bedrock type, soil texture, soil organic and fertilizer application were identified as the main factors influencing transfer factors of heavy metals from soil to tea. The specific types of tea grown in the soil with sandy clay and bedrock of granite/granodiorite and shale should be given more monitoring. The non-carcinogenic hazard quotients (HQ) and cancer risk (Risk) through tea drinking were primarily caused by Pb and Cd respectively. To reduce the potential health risk from tea, application of organic and/or compound fertilizer were thought to be the effective management strategy for tea plantation. [ABSTRACT FROM AUTHOR]

• Soil hydrological properties (HPs) were determined using borehole nuclear magnetic resonance technique. • Fractal and multifractal dimensions are effective parameters for estimating soil HPs. • Capillary water dominates soil total water in alpine soils. • Alpine vegetation alters the relationship between soil PSD and HPs. The soil hydrological properties (HPs) in active layers regulate soil water migration and affect the evolution of permafrost and biogeochemical cycles. There is relatively little understanding of the changes in soil HPs as a result of soil particle-size distribution (PSD) in the permafrost regions of the Qinghai–Tibet Plateau. In this study, different land-cover types, namely alpine wet meadow (AWM), extremely degraded wet meadow (EDWM), alpine meadow (AM), degraded alpine meadow (DAM), alpine steppe (AS), and alpine desert (AD), were used to determine the relationships between soil PSD and HPs. Soil HPs were determined using borehole nuclear magnetic resonance, and soil PSD (0–2 mm) was analyzed using fractal and multifractal theory. The results showed that vegetation degradation caused coarse soil particle accumulation in the root zone, reflected by the soil single-fractal dimension (D v : 2.12–2.50). The D v values showed significant positive correlations with soil clay and silt content as well as a negative correlation with sand content. Results from the generalized fractal and singularity spectra suggested an even distribution of soil particles in the root zone of the AWM, AM, and AD sites. Vegetation degradation increased the soil PSD capacity dimension (D 0), information dimension (D 1), correlation dimension, D 1 / D 0 ratio, and Hölder exponent of order zero. This was indicative of a narrow soil PSD range and non-uniform soil texture in the root zone. Although capillary water dominated the total soil water content in the alpine soils, soil water composition was also dependent on the vegetation type and soil stratigraphic distribution. Soil particle composition and multifractal dimensions were found to be effective parameters for forecasting soil HPs in the non-root zone of alpine soils. However, the presence of vegetation weakens the relationship between soil PSD and HPs. This study contributes to the accurate evaluation of hydrological and biogeochemical cycles in permafrost regions. [ABSTRACT FROM AUTHOR]

• Uniform standard developed for the saline soil samples with surface cracks. • Wavelet texture features extracted from cracked patterns of soil samples. • Quantitative analysis carried out between EC and wavelet texture features. • A new quick and non-destructive method developed for EC measurement. Wavelet texture features can well describe the cracking of salt-affected clayey soils on different decomposition scales since the desiccation cracking is considered as a common phenomenon and mainly determined by the salt content. To establish the relationship between wavelet texture features and the salinity of soda saline-alkali soils, 200 soil samples were selected in Songnen Plain of China and the crack images of the samples were processed uniformly. The 4-levels orthogonal wavelet decompositions were performed based on coiflet-1 wavelet basis function using the grayscale images. After that, correlation analysis was carried out between electrical conductivity (EC) and wavelet texture features (energy and L1 norm) under different decomposition levels. The results indicate that the poor relationship between low-frequency texture features and EC is hardly affected by the decomposition levels, but the correlation coefficients between high-frequency wavelet texture features and EC of soil samples increases significantly with decomposition levels. Besides, 100 calibration samples were used to establish the regression models and the results show that both energy and L1 norm are exponentially correlated with EC of soil samples especially for those from 90° high-frequency decomposition results with R2 of the exponential models of 0.90 and 0.84. A fast EC measurement method for predicting soil EC was then proposed and verified by the other 100 soil samples. The fitting results show very high prediction accuracy when EC was calculated by the energy from 90° with R2 of 0.91 and ratio of performance to deviation (RPD) of 4.73 and L1 norm from 90° with R2 of 0.85 and RPD of 3.53. Moreover, the fitting results based on the mean texture features calculated from 0°, 90° and 135° high-frequency decomposition results are also relatively good (R2 of 0.88 and RPD of 4.13 for energy, R2 of 0.81 and RPD of 3.36 for L1 norm). [ABSTRACT FROM AUTHOR]

• SEM analyses explained 12.0–46% of the variations in soil K. • Climate acted as the most important factor controlling the variations in soil K. • Topographical conditions were the secondary controls of soil K variations. • Key soil properties and clay mineral showed less effect on soil K variations. • Climate, topography and clay mineral all exhibited indirect effect on soil K variations. Climatic, topographical and soil conditions are the main drivers of soil potassium (K) variations in terrestrial ecosystem. Although theoretical and empirical studies have explored the single effect of these factors on the variations of soil K, the complex interactions and relative importance of these factors is scarce worldwide and virtually absent for China agricultural ecosystem. Here, the complex interactions and the relative contributions of the environmental variables (climate, topography, key soil properties and clay mineralogical composition) to soil K variations were evaluated in China agricultural soil by using method of structural equation model (SEM). The SEM analyses explained 12.0%, 46% and 28.8% of the variations in soil exchangeable K (EK), nonexchangeable K (NEK) and total K (TK), respectively. The results also showed that climate acted as the most important factor controlling soil K variations, followed by topographical conditions, clay mineralogical composition, and key soil properties. High temperature and precipitation (climate) had directly negative effects on soil K concentrations and the negative effects were strengthened by its impacts on key soil properties and clay mineralogical composition. The effects of topography on soil K concentrations were enhanced by its effects on climate, key soil properties and soil clay mineralogical composition. Soil clay mineralogical composition affected soil K concentrations both directly and indirectly through influencing key soil properties. The unexplained variations in soil K concentrations are due to lack of data related to crop species, finer soil particles content, and the quantity and quality of K inputs. These findings advance the understanding of the patterns and mechanisms driving soil K variations, which is critical for predicting changes in soil nutrients in response to soil forming environment at the global scale. [ABSTRACT FROM AUTHOR]

• Controlling factors of organic carbon and nitrogen in alpine meadows were determined. • Grazing exclusion does not increase soil organic carbon and total nitrogen. • Soil organic carbon was explained by interaction between vegetation and soil. • Biomass, cover, soil moisture and clay were key factors affecting organic carbon. The accrual of soil organic carbon (SOC) and nitrogen (N) in grassland is an important management option to improve the ecosystem functions of grassland. However, how abiotic (such as grazing exclusion (GE)) and biotic factors influence SOC and N and their different fractions in Tibetan alpine meadows remains unclear. In this study, we evaluated the relative importance of abiotic and biotic factors that drive SOC and N contents in soil density fractions by performing redundancy analysis based on three long-term (10 years) fenced alpine meadows maintained in the permafrost region of the Tibetan Plateau in China. Biotic factors comprise plant aboveground biomass, cover and diversity, whereas abiotic factors include soil properties (i.e. soil moisture, pH, clay, silt, sand, total phosphorus, available phosphorus, microbial biomass carbon and N, available N, C:N ratio and C:P ratio) and GE. Site rather than GE has significant effects on the SOC and N contents. GE caused no increase in the SOC and N contents in the whole soil and fractions. Redundancy analysis showed that 96.7% of the variations in SOC and N fractions can be explained by the selected explanatory variables. Aboveground biomass, cover, soil moisture and clay contents were key factors that affected the SOC and N fractions. The SOC and N fractions were mainly explained by the interaction between vegetation and soil, followed by soil, vegetation and GE. The study highlighted the importance of considering the covariation of vegetation and soil for evaluating the SOC and N dynamics in alpine meadows. The effect of GE (such as 10 years) on the SOC and N contents in alpine meadows can be weak in the permafrost region of the Tibetan Plateau. [ABSTRACT FROM AUTHOR]

• Particle characteristics of clay rock derived soils were analyzed. • A determination method of multi-mineral sand particles (MSPs) was established. • MSP content in shale-derived soils was higher than that in mudstone-derived soils. • Characteristics of clay rock soils lie on the process of diagenesis and pedogenesis. Multi-mineral sand particles (MSPs), commonly found in upland soils, can change the erosion properties, structure, moisture level, porosity, and permeability of soil; however, their effects are generally neglected in previous studies. In this study, we explored the morphology using scanning electron microscopy (SEM), particle size distribution (PSD), aggregation state, and mineralogy of soils derived from two types of clay rocks containing MSPs: shale and mudstone. The results showed that: (1) small lamellate bodies formed granules and blocks in a face-to-face or side-to-side manner and that the aggregation particles ranged from several to tens of microns in diameter, which increased gradually in a downslope direction; (2) the sand content in shale- and mudstone-derived soils decreased from 41.0% and 31.3%, respectively, on the summit to 19.6% and 18.4%, respectively, on the toeslope, whereas their clay content increased from 23.3% and 20.2% to 45.0% and 38.9%, respectively; (3) regarding the aggregation states of soil particles, the content of 0.25–2 mm MSPs in the shale- and mudstone-derived soils decreased from 62.9% and 45.2%, respectively, on the summit to 7.1% and 1.4%, respectively, on the toeslope, with averages of 42.3% and 20.8%, respectively. The content of 0.25–2 mm aggregates in the shale- and mudstone-derived soils increased from 9.1% and 6.2%, respectively, on the summit to 44.4% and 21.1%, respectively, on the toeslope, with averages of 21.5% and 14.2%, respectively; and (4) the mineralogy of the clay rock-derived soils and MSPs was generally dominated by illite, montmorillonite, vermiculite and calcite, which was similar to the mineralogy of the parent rocks. Therefore, a large amount of MSPs was found in clay rock-derived soils whose particle characteristics were determined by the environment of diagenesis and the physical weathering of pedogenesis. [ABSTRACT FROM AUTHOR]

• SOC in the collapsing gully was significantly lower than that in the hillslope. • There was no organic carbon enrichment in the alluvial fan and check dam. • The loss of soil clay and iron oxides in collapsed soil intensified SOC erosion. • Collapsing gullies deteriorated soil properties and accelerated SOC loss. Collapsing gullies are one of the most serious soil erosion problems in the tropical and subtropical areas of South China. However, few studies have determined the effects of collapsing gullies on the redistribution and loss of soil organic carbon (SOC) in the red soil hilly region. This study investigated the variations in different kinds of SOC in a collapsing gully and a hillslope and the relationships between various soil properties and SOC. The results showed that the dissolved organic carbon (DOC), particulate organic carbon (POC), readily oxidizable organic carbon (ROOC) and total organic carbon (TOC) contents on the hillslope were higher than those in the collapsing gully. Below the location of upper catchment in the collapsing gully, the DOC, POC, ROOC and TOC contents were all greatly reduced, and there was no organic carbon enrichment in the alluvial fan and check dam. The stability of SOC in the collapsing gully was lower than that in the hillslope. The average free iron oxides (Fe d), organically bound iron oxides (Fe p) and clay contents in the collapsed soil were much lower than those on the hillslope. SOC content was significantly and positively correlated with the soil Fe d , Fe p and soil clay contents but negatively correlated with soil pH. Among these soil parameters, the dominant factors influencing TOC in the red soil hilly region were soil ROOC and soil pH. The SOC density of 0–30 cm soil in the collapsing gully was equivalent to nearly 15.9% of that in the hillslope. These results demonstrate that collapsing gullies have highly deteriorated soil properties and are therefore subject to accelerated SOC loss in the red soil hilly region. [ABSTRACT FROM AUTHOR]

Vegetation restoration affects the stability of soil organic carbon (SOC) by changing the composition of soil carbon pools, including active carbon (C a), the labile pool of SOC; slow carbon (C s), the physically stabilized pool of SOC; and resistant carbon (C r), the chemically stabilized pool of SOC. The aims of this study were to determine how SOC pools changed during restoration of a subtropical forest and to what extent vegetation characteristics and soil properties affected the changes in SOC pools. Soil samples were collected to 40 cm in four plant communities along a restoration chronosequence: scrub-grassland (4–5 years), shrubs (10–12 years), coniferous and broadleaved mixed forest (45–46 years), and evergreen broadleaved forest (90–91 years). Laboratory incubations were used to measure CO 2 production during SOC mineralization, and acid hydrolysis was used to measure C r. The CO 2 production and C r data were fitted to a three-component first-order kinetic model to determine the C a and C s. Pearson's correlations, stepwise multiple line regressions, and variation partitioning analysis were used to determine the key factors that affected SOC pools. The results showed that vegetation restoration increased the contents of SOC from 1.67 to 47.6 g kg−1, C a from 0.03 to 0.35 g kg−1, C s from 1.32 to 24.5 g kg−1, and C r from 0.33 to 22.8 g kg−1. During vegetation restoration, the increase in SOC was primarily due to carbon (C) stored in stable pools (i.e., C s or C r), and the portion of C r in total SOC increased markedly from 18.5 to 56.3%. Fine root biomass was the primary driver that controlled SOC pools during vegetation restoration. The C/N ratio of litter had a greater effect on C a and C s than that of other factors, whereas the soil clay content contributed secondarily to C r. The results suggest that vegetation restoration increases not only the amounts of SOC, C a , C s , and C r but also the stability of the SOC pool in subtropical soil. The relatively rapid increases in C s and C r following vegetation restoration played a crucial role in C sequestration. Therefore, strong measures to preserve natural forests and facilitate vegetation restoration should be the primary approach to increase long-term soil C sequestration in this region. • Soil organic carbon (SOC) content increased as vegetation restoration proceeded. • The increased SOC was mainly stored in the more stable carbon (C) pools. • Rapid increases in resistant C to SOC ratio played a crucial role in C stabilization. • Fine root biomass was the primary driver of the increased SOC pools with restoration. [ABSTRACT FROM AUTHOR]