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Aims: Karst ecological restoration (KER) publication characteristics, topic trends, and knowledge domains were analysed to provide a global perspective. Methods: Bibliometric and knowledge map analyses were used to analyse KER documents (319) in the WoSCC. The whole period was divided into the germination (GP), slow growth (SGP) and rapid growth (RGP) periods based on the number of annual publications (NAP). Results: (1) The NAP increased over time, with China contributing the most. (2) The study topics varied and flourished over time. Plant was the most studied class and Animal the least studied in the Biology category. In the Environment category, Water was the most studied medium in the GP, while Soil was the most studied in the SGP and RGP. Remote sensing and Model were the leading methods in the SGP and RGP; Field investigation and/or experimental methods, including Leaf traits, Vegetation investigation, and Chlorophyll fluorescence, were the main methods in the GP. Ecological engineering was the leading restoration method overall. Planting pattern was a new restoration method in the SGP, while Biochar, Seed bank, and Soil translocation were new methods in the RGP. (3) Eleven knowledge domains and 10 vital documents well support studies on KER. Future research directions are proposed. Conclusions: The results provide a new, global, objective perspective for understanding KER research over the past 3 decades. [ABSTRACT FROM AUTHOR]

Aims: Larix kaempferi planting with broad-leaved trees can increase production and alleviate soil degradation; however, the mechanism is unclear, especially on large scales and in different climate regions. This paper attempts to explain the underlying mechanism in a temperate region and northern subtropical alpine region of China. Methods: Litter decomposition rates, nutrient release, enzyme activity and microbial community composition were determined in conifer litter, broad-leaved litter and mixed litter by the litterbag method during about 500 days in the two regions. Results: Decomposition rate was increased by 4.00% in temperate region and 3.38% in the subtropical region after litter mixing and the synergistic effect increased with decomposition progress. However, nutrients release was not always enhanced, and enzyme activities were enhanced at the most of decomposition time and higher in the subtropical region. After litter mixing, a few new dominant taxa emerged, and the microbial gene quantities were increased in the temperate region, but not in the subtropical region. The dominant bacterial taxa were similar, while most of the dominant fungal taxa shifted with decomposition. In addition, the dominant fungi completely differed between the two regions. The environmental variables with greater influence on microbial community were similar in the two regions, including C:N, C:P and pH. Conclusions: After mixing with broad-leaved litter, the decomposition of Larix kaempferi was enhanced by increasing enzyme activities and microbial quantities in the temperate region, but the mechanisms were not clear in the subtropical region. [ABSTRACT FROM AUTHOR]

Background and aims: Precipitation and nitrogen (N) deposition are predicted to increase in northern China. The present paper aimed to better understand how different dominant species in semi-arid grasslands in this region vary in their litter decomposition and nutrient release responses to increases in precipitation and N deposition. Methods: Above-ground litter of three dominant species (two grasses, Agropyron cristatum and Stipa krylovii, and one forb, Artemisia frigida) was collected from areas without experimental treatments in a semi-arid grassland in Inner Mongolia. Litter decomposition was studied over three years to determine the effects of water and N addition on litter decomposition rate and nutrient dynamics. Results: Litter mass loss and nutrient release were faster for the forb species than for the two grasses during decomposition. Both water and N addition increased litter mass loss of the grass A. cristatum, while the treatments showed no impacts on that of the forb A. frigida. Supplemental N had time-dependent, positive effects on litter mass loss of the grass S. krylovii. During the three-year decomposition study, the release of N from litter was inhibited by N addition for the three species, and it was promoted by water addition for the two grasses. Across all treatments, N and potassium (K) were released from the litter of all three species, whereas calcium (Ca) was accumulated. Phosphorus (P) and magnesium (Mg) were released from the forb litter but accumulated in the grass litter after three years of decomposition. Conclusions: Our findings revealed that the litter decomposition response to water and N supplementation differed among dominant plant species in a semi-arid grassland, indicating that changes in dominant plant species induced by projected increases in precipitation and N deposition are likely to affect litter decomposition, nutrient cycling, and further biogeochemical cycles in this grassland. The asynchronous nutrient release of different species' litter found in the present study highlights the complexity of nutrient replenishment from litter decomposition in the temperate steppe under scenarios of enhancing precipitation and N deposition. [ABSTRACT FROM AUTHOR]

Aims: Fertilization methods have affected the development of dryland agriculture. There is a need to understand the impacts of different fertilizer application depths on crop production and gas emissions to facilitate the sustainable development of dryland agriculture. Methods: A field experiment was conducted for two years (2019–2020) in a dryland agroecosystem in the Loess Plateau region of China. Five fertilizer placement depths were tested comprising 0 cm (FD0), 5 cm (FD5), 15 cm (FD15), 25 cm (FD25), and 35 cm (FD35). N-P-K fertilizer was applied to all treatments as base fertilizer at the same rate. After sowing, the gas emission fluxes were measured 17 consecutive times. We systematically analyzed the effects of different fertilization depths on the summer maize (Zhengdan 958) yield, ammonia (NH3) volatilization, and greenhouse gas emissions (nitrous oxide (N2O), carbon dioxide (CO2), and methane (CH4)). Results: The results showed that the NH3 volatilization, N2O emissions, CO2 emissions, and global warming potential (GWP) decreased as the fertilization depth increased. Compared with the traditional fertilization depth (FD5), deep fertilization at 15 cm clearly reduced the NH3 volatilization, N2O emissions, CO2 emissions, GWP, and greenhouse gas intensity. In addition, compared with FD25 or FD35, FD15 increased the capacity of the soil to absorb CH4. Critically, compared with the traditional fertilization depth, FD15 can effectively improve the summer maize biomass yield (4.2%) and grain yield (18.1%) at the final harvest. Conclusion: FD15 can promote the sustainable development of dryland agriculture in the Loess Plateau region of China by improving crop production and reducing gas emissions. [ABSTRACT FROM AUTHOR]

Aims: Lakeshore wetlands are global carbon (C) hotspots, but their role in C sequestration has been largely overlooked. The rhizosphere has a complex interaction of microbiota and metabolites, which plays an important role in wetland C cycling. This study aims to understand how the rhizospheric interactions affect harvested aboveground C and soil C of lakeshore wetlands in a subtropical region. Methods: An investigation of five lakeshore reed (Phragmites australis) wetlands at the similar latitudes of the Lower Yangtse Valley in China was carried out to explore the relationship of rhizospheric interactions with harvested aboveground C and soil C. The plant traits and soil physicochemical properties were determined due to their important role in affecting rhizosphere interactions. Results: Plant traits and soil physicochemical properties significantly differed among the sites, while aboveground C fixation did not significantly differ. The soil organic C (SOC) content of the topsoil was accounting for the majority of the soil total C at most sites, except for the wetland at the Yangtze River estuary with higher soil pH and conductivity, whose soil inorganic C (SIC) accounted for almost half. Bacterial community and metabolite composition were significantly partitioned across the region. Structural equation modeling revealed the rhizospheric interactions positively affected aboveground C and SOC, but negatively affected SIC. Their effects on soil C content were stronger than those on aboveground C fixation. Conclusions: The rhizosphere exhibited the direct and indirect effects on harvested aboveground C and soil C by altering microbial community structure and metabolite composition. [ABSTRACT FROM AUTHOR]

Aims: Film mulching has been widely used for increasing crop yields in semiarid areas, but its long-term impact on crop performance and soil quality remains poor. This study aims at investigating the long-term effects of different mulching methods on the crop root growth and soil aggregates stability. Methods: A continuous experiment for eight years was set to assess the effects on the soil aggregates stability, root traits, and yield under five different treatments: (i) control method comprising flat planting without mulching (CK), (ii) flat planting with half film mulching (P), (iii) film mulching on ridges and planting in narrow furrows (S), (iv) full film mulching on double ridges (D), and (v) film mulching on ridges and planting in wide furrows (R). Results: The soil quality improved significantly after continuous film mulching for eight years. Compared with CK, mulching decreased the soil bulk density, and increased the soil porosity, soil macroaggregate content (7.39%-22.92% by dry-sieving, and 8.49%-21.67% by wet-sieving), and soil aggregate stability, especially under S and D. Mulching could promote the root growth (root length, root diameter, root surface area, and root volume) distinctly, while S and D increased the average root biomass by 17.27% compared with R and P. The improved soil structure and root traits under mulching increased the yield (29.98–63.96%), and the average yield under S was 1.32%, 25.7%, and 26.14% higher than those under D, R, and P, respectively. Conclusions: In general, the best improved soil aggregate fractions and stability was found under film mulching on ridges and planting in narrow furrows (S), which was significantly associated with the root traits improvement, and thus increasing the crop yield. Therefore, it can be considered an effective mulching pattern for increasing and stabilizing the crop yield in the Loess Plateau region of China. [ABSTRACT FROM AUTHOR]

Background and aims: Phosphorus (P) fertilization affects plant diversity and ecosystem function by changing the abundance and composition of functional soil microorganisms and genes. Understanding the mechanisms regulating the soil carbon (C), nitrogen (N), sulfur (S), and P cycle across different P fertilizer inputs is crucial to the management of P in sustainable agroecosystems. Methods: We investigated whether soil functional microorganisms affected the coupling of the abundance of soil C, N, P, and S genes under long-term (up to 14 years) P fertilizer input (0, 21.8, 43.6, and 87.2 kg P ha−1 yr−1) on the Loess Plateau of China. Results: Long-term P fertilizer input resulted in the increased abundance of soil functional microorganisms and the expression of soil C cycle genes but decreased soil P cycle genes. The relative abundance of ecological clusters (including bacteria, fungi, and archaea) was significantly correlated with functional genes related to the C, N, P, and S cycles. Soil Actinobacteria, Proteobacteria, Cyanobacteria, Bacteroidetes, and Chloroflexi were the keystone taxa mediating soil nutrient cycling in wheat fields. Both Mantel's test and structural equation modeling indicated that the shifts in soil available C and P were the major factors driving the coupling of soil functional microorganisms and genes. Conclusions: The changes in soil microorganisms and genes can drive soil nutrient cycling and promote crop growth, suggesting that their relationship can provide new insight for understanding the microbial mechanisms of soil P turnover in sustainable agroecosystems. [ABSTRACT FROM AUTHOR]

Purpose: Dissolved organic matter (DOM) plays a key role in agroecosystems' carbon cycling. However, the DOM evolutionary signatures and the timing of equilibrium being achieved in dryland inter-planting systems remain unclear. This study aimed to determine the characteristics of DOM dynamics using a three-dimensional fluorescence excitation-emission matrix combined with parallel factor analysis (EEMs-PARAFAC). Methods: DOM contents, different related components accumulation were assessed using clear tillage (CT) as the control, white clover (Trifolium repens L.) of three different ages (4, 8, 12 years), representing a chronosequence, in apple orchards on the Loess Plateau. Results: At a depth of 0–10 cm, DOM concentration decreased with depth and significantly increased with longer inter-planting, and the five fluorescence components contents of soil DOM showed a similar trend. Moreover, the relative abundances of humic-like (C2, C3) was higher than CT, but the protein-like was lower. The ultraviolet–visible spectral and optical indices indicated that DOM mainly originated from mixed sources, and gradually tended towards greater DOM molecular complexity with increasing time since sowing. Microbial biomass nitrogen and soil organic carbon (SOC) were the most important two factors affecting DOM over time, contributing to 87% and 77% of the total variation. Conclusions: This study demonstrated that inter-planting time and soil depth played important roles in determining DOM content and component accumulation. Overall, inter-planting with white clover in orchards can effectively improve the accumulation of macro-molecular humic-like DOM, which probably promotes SOC storage. Long-term experiments are required exploring DOM dynamics and the timing of equilibrium being reached. [ABSTRACT FROM AUTHOR]

Aims: To demonstrate how intensive management practices affect the belowground productivity of Moso bamboo, we examined the spatial distribution of fine root traits under three stands with high-intensity (T1, tillage plus biennial fertilization), low-intensity (T2, tillage plus quadrennial fertilization), and extensive (CK, no-tillage plus no fertilization) management, and evaluated the relationships among root traits and soil properties, aggregate stability (MWD). Methods: Bamboo fine root and soil samples were collected from three depths (0–10, 10–20, 20–30 cm) and three horizontal distances (20, 40, 60 cm) under three management strategies. Root biomass, root morphology, soil properties, and aggregate composition were determined. Results: Compared with CK, T1 and T2 had higher fine root biomass (FRB), and the largest FRB in the 10–20 cm soil layer. T1 had significantly higher allocation proportion of D1–2 class FRB and root length density (RLD) and significantly lower specific root length (SRL) and specific surface area (SSA). Vertically, intensive management led to an increase in FRB in the 10–20-cm soil layer and MWD in the 20–30-cm soil layer. Horizontally, FRB was highest at a distance of 20 cm from bamboo culm. A strong positive correlation was identified among FRB, RLD, and TP in each soil layer as well as among MWD, TP, and RLD. Conclusions: Intensive management promotes fine root growth with high length in response to more soil P content, and high-intensity management shifts the expression of root functional traits toward transport fine roots proportion and 10–20-cm soil layer, and facilitates aboveground productivity of Moso bamboo. TOC, TP, and RLD are the main three drivers correlated with soil aggregate stability. [ABSTRACT FROM AUTHOR]

Aims: An in-depth understanding of the relationship between the theoretical carrying capacity of grasslands and the forage-livestock balance is crucial for maintaining ecological equilibrium in grasslands and guiding ecological engineering. However, the spatiotemporal patterns of these two parameters in the arid mountainous region of the Qilian Mountains (QLMs) in China remain unclear. Methods: The Carnegie-Ames-Stanford approach (CASA) model was employed to estimate the theoretical carrying capacity. The grazing pressure index, which represents the ratio of the actual to theoretical carrying capacity, was used to assess the forage-livestock balance. Results: From 2000 to 2018, the theoretical carrying capacity of grasslands in the QLMs showed a significant (p < 0.01) increasing trend (0.011 ± 0.002 standard sheep unit (SU)·ha−1·yr−1), with an average value of 0.73 ± 0.7 SU·ha−1. Its spatial distribution was high in the southeast and low in the northwest of the QLMs. The total annual precipitation of 72.1% in the grasslands was significantly and positively correlated with the theoretical carrying capacity (R = 0.45; p < 0.05). The average grazing pressure index of natural grasslands in the QLMs was 2.08 ± 0.14, indicating that the grasslands were generally overloaded. The value increased significantly (p < 0.05) from 2000 to 2010 but has been decreasing significantly since 2011. Spatially, overloading was more severe in the southeastern counties. Conclusion: Precipitation was the main factor responsible for the increase in the theoretical carrying capacity of the grasslands. In future grassland management, the red early-warning zones exhibiting continuously increasing overloading should be prioritized. [ABSTRACT FROM AUTHOR]

Background and aims: Soil seed bank plays a significant role in the natural recovery and the succession of forest. A large number of natural secondary forests are distributed in the Qining Mountains, China. However, it remains unclear how the soil seed banks develop and influence the recovery of secondary forests. Methods: We explored the aboveground vegetation and soil seed bank at 27 plots along forest developmental stages of pine and oak forests in the Qinling Mountains. Species composition and abundance of aboveground vegetation as well as seed bank composition and density were surveyed and their correlations with forest developmental stages were determined. Results: The results showed that the species richness of seed banks was the highest in middle-aged forests, as well as the aboveground vegetation. The seed density and abundance increased with forest developmental stages and varied among different forest types. The similarity between seed banks at different developmental stages of the same forest type was high, as well as aboveground vegetation. The seed bank and aboveground vegetation showed low similarity across the three developmental stages of both forest types, and the persistent soil seed bank did not reflect the changes in aboveground vegetation. Conclusion: Our findings demonstrate that developmental stages play an important role in the composition of seed banks and aboveground vegetation. Our results also highlight the persistent soil seed bank contributes less to the forest recovery. We can assume that the natural recovery of disturbed natural secondary forests is largely dependent on transient soil seed bank and seed dispersal. [ABSTRACT FROM AUTHOR]

Aims: Nitrogen (N) deposition alters plant stoichiometry and the state of nutrient limitation in forest ecosystems. In subtropical forests of China, responses of plants stoichiometry to chronically elevated and recently declined N deposition remain unclear. Methods: A 14-year investigation of needle elements, including N, phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg) and aluminum (Al), was carried out under field N manipulation (10-year N addition and subsequent cessation of N addition) in a typical, subtropical Masson pine (Pinus massoniana Lamb.) forest in southwest China. Results: Needle N and P concentrations were significantly elevated by N addition even after N addition ceased while needle N:P remained constant among treatments. Needle N:K and P:K were significantly elevated by N addition, but were no longer different from reference plots after N addition ceased. Masson pine's annual relative growth rate (RGR) was significantly decreased by N addition but the differences among treatments became insignificant among treatments after N addition ceased. Additionally, the annual RGR was negatively correlated with needle Al concentration. Needle Al exhibited a trend of first rising and then decreasing over the 14-year experiment. Conclusions: Under the background of high ambient N deposition and Ca deposition, chronic N addition does not aggravate P limitation but can result in K limitation in a N-saturated subtropical forest. With the recovery of subtropical forest from soil acidification and N saturation, the elevated needle N and P induced by N addition will persist for at least four years and most likely for much longer in the future, but the risk of K limitation is expected to diminish. [ABSTRACT FROM AUTHOR]

Background and Aims Pinus massoniana: Lamb. is an important conifer forestry species in south China, but soil fertility has declined over time in monoculture plantations. Knowledge about how P. massoniana uses phosphorus (P) by distributing it among five biochemical fractions and how intercropping with broadleaf Castanopsis hystrix alters that pattern may inform long-term plantation management. Methods: We studied a single P. massoniana plantation that was split in half into a monoculture and a P. massoniana / C. hystrix intercropped plantation 25 years after establishment. We measured photosynthesis and leaf concentrations of total P, P allocated to five chemical fractions and total nitrogen (N). We also measured soil N concentrations. Results: Intercropping C. hystrix with 25-year-old P. massoniana for a further 34 years had no significant impact on P. massoniana total stem volume, although intercropped P. massoniana trees were 5 m taller. Intercropping with C. hystrix increased timber biomass due to the additional C. hystrix stems. Growth of C. hystrix was likely more limited by P than that of P. massoniana in both plantations. Total P concentration and its allocation among fractions declined with increasing leaf age, but differed in the two species. Leaf P-resorption efficiency in intercropped P. massoniana was 79%, which was about 15% greater than that in P. massoniana monoculture and in the intercropped C. hystrix. The greater P-resorption efficiency in intercropped P. massoniana than in monoculture was due to greater mobilization of P from all fractions, except phospholipids. Bulk soil N concentration was 50% greater in the intercropped plantation than in monoculture. Conclusion: Adding C. hystrix to an P. massoniana plantation was effective at increasing wood yield without compromising productivity of P. massoniana. [ABSTRACT FROM AUTHOR]

Background: Mixed plantations utilize resources through specific strategies. However, the impact mechanism of mixed plantations on the water and nutrient use efficiency of different tree species remains unclear. Methods: Robinia pseudoacacia mixed (R. pseudoacacia and Amygdalus davidiana, RPAD; R. pseudoacacia and Armeniaca sibirica, RPAS) and monoculture stands (R. pseudoacacia, RP; A. davidiana, AD; and A. sibirica, AS) were used to determine mixing species relative to monoculture effects on leaf water (WUE), nitrogen (NUE), and phosphorus (PUE) use efficiencies and their potential drivers in the Loess Hilly Region. Results: Mixing R. pseudoacacia and A. sibirica is a good strategy to maximize soil nutrient resources. Compared to monocultures of all species, R. pseudoacacia and A. davidiana in RPAD and A. sibirica in RPAS had higher WUE and lower NUE and PUE; P limitation of R. pseudoacacia in mixed stands was lower than that in RP. Furthermore, R. pseudoacacia WUE was positively correlated with stand density and crown area, A. davidiana and A. sibirica were the opposite. Regarding all tree species, WUE was influenced by leaf dry matter content, leaf tissue density, and soil available P, while NUE, PUE, and N:P ratio were by average tree height and specific leaf area. Notably, irrespective of tree species, WUE exhibited a negative correlation with NUE and PUE, but a positive correlation with N:P ratio. Conclusions: Mixed plantations affect water and nutrient use efficiency by altering the above- and below-ground niche through tree structure, and there is a degree of trade-off between WUE, and NUE, PUE. [ABSTRACT FROM AUTHOR]

Background and aims: The impact of understory vegetation control or replacement with selected plant species, which are common forest plantation management practices, on soil C pool and greenhouse gas (GHG, including CO, CH and NO) emissions are poorly understood. The objective of this paper was to investigate the effects of understory vegetation management on the dynamics of soil GHG emissions and labile C pools in an intensively managed Chinese chestnut ( Castanea mollissima Blume) plantation in subtropical China. Methods: A 12-month field experiment was conducted to study the dynamics of soil labile C pools and GHG emissions in a Chinese chestnut plantation under four different understory management practices: control (Control), understory removal (UR), replacement of understory vegetation with Medicago sativa L. (MS), and replacement with Lolium perenne L. (LP). Soil GHG emissions were determined using the static chamber/GC technique. Results: Understory management did not change the seasonal pattern of soil GHG emissions; however, as compared with the Control, the UR treatment increased soil CO and NO emissions and CH uptake, and the MS and LP treatments increased CO and NO emissions and reduced CH uptake ( P < 0.05 for all treatment effects, same below). The total global warming potential (GWP) of GHG emissions in the Control, UR, MS, and LP treatments were 36.56, 39.40, 42.36, and 42.99 Mg CO equivalent (CO-e) ha year, respectively, with CO emission accounting for more than 95 % of total GWP regardless of the understory management treatment. The MS and LP treatments increased soil organic C (SOC), total N (TN), soil water soluble organic C (WSOC) and microbial biomass C (MBC), while the UR treatment decreased SOC, TN and NO-N but had no effect on WSOC and MBC. Soil GHG emissions were correlated with soil temperature and WSOC across the treatments, but had no relationship with soil moisture content and MBC. Conclusions: Although replacing competitive understory vegetation with legume or less competitive non-legume species increased soil GHG emissions and total GWP, such treatments also increased soil C and N pools and are therefore beneficial for increasing soil C storage, maintaining soil fertility, and enhancing the productivity of Chinese chestnut plantations. [ABSTRACT FROM AUTHOR]

For establishing rational farming mechanism, it is essential to know the relative contribution of different geological background and anthropogenic activities to trace elements in agricultural soil. In this paper, 282 surface soil samples were collected based on the different geological background. Five harmful trace elements (As, Cd, Cr, Hg and Pb) were analyzed. The results indicated most of trace elements contents were far beyond the threshold of uncultivated soil background, which indicate anthropogenic input strongly influenced on trace elements in agricultural soil. In addition, correlation analysis showed trace element contents exhibited high relationships with soil pH, C/N and physical clay (<0.01 mm) ( p < 0.05). The principal component analysis showed that the first component included Cd, Cr and Hg, while Pb and As formed the second component. Furthermore, in the agricultural topsoil derived from carbonate rock, the high background values of trace elements and alkaline condition made the enrichments of Cd, Cr and Hg were the most significant. In the agricultural topsoil derived from red residua, the Pb and As contents was the highest values among the soil categories, partly because the type of soil had amount of physical clay (<0.01 mm). In the agricultural topsoil derived from shale, the pH or physical clay had significant relationship with Cd, Pb, Hg and As ( p < 0.01). In the agricultural topsoil derived from sand stone, the acid condition and loose texture might account for the lowest values of Cd, Cr, Pb and As content to some extent. [ABSTRACT FROM AUTHOR]

Little is known about the soils that support agriculture in Tibet. The aim of this paper is to investigate the physical and chemical properties of Tibet's agricultural soils, the nutritional status of wheat ( Triticum aestivum L.) and barley ( Hordeum vulgare L.) crops, and the sustainability of current soil management practices. Physical descriptions of Tibet's agricultural soils were based on soil pits dug at three locations across Tibet's agricultural zone. Chemical analyses were conducted on soils from seven sites across the zone. Nutritional constraints to agriculture were identified through leaf tissue tests on wheat and barley crops from 23 fields. These results, combined with published information on farm inputs and yields, provided insight into the sustainability of current nutrient practice. Soils were found to be silty or sandy clay loams with alkaline reaction, low organic content and low K and Zn status. Leaf analysis revealed one third to one half of cereal crops were marginal or deficient for K, Zn and Mg. Most farmers export grain and import only nitrogenous and phosphatic fertilizers leading to a nutrient imbalance. A balanced fertilizer program is required to halt nutrient depletion and increase grain production. Reduced tillage and crop residue retention are needed to improve soil health. [ABSTRACT FROM AUTHOR]

Long-term monitoring of soil properties reveals site-specific ecosystem shifts in soil processes due to land use and climate changes. This paper aims to study the effects of physical landscape changes associated with grazing on soil thermal and moisture regime at the plot scale in a semiarid Leymus chinensis steppe of Inner Mongolia, China. The investigated sites were subjected to three grazing intensities: ungrazed since 1979 (UG79), moderately grazed only in winter time (WG), and heavily grazed (HG). At each plot, we recorded the soil moisture and temperature over a 6-year period that spanned between June 2004 and September 2009 and experienced a large range in precipitation (162 to 362 mm). Based on these monitoring data, we divided a year into four hydric periods: (1) growing period (late April to August); (2) transitional period from summer to winter (September-October); (3) winter time (November-first March); and (4) transitional period from winter to summer (March-April). In general, soil moisture in grazed sites was lower than in the ungrazed site, particularly for the 30-50 cm soil layer. Seasonal fluctuation of the soil moisture, due to variable precipitation and atmospheric demands, was most significant in the topsoil (0-10 cm) and was less pronounced in deeper soil. Regardless of hydric seasons, soil moisture was significantly influenced by grazing intensity, whereas soil temperature was slightly influenced. With increasing grazing intensity, soil water storage decreased remarkably. Consequently, grazing reduced plant available water and therefore grassland productivity, which are linked to a great extent with the trampling-induced soil structure change and soil moisture regime. [ABSTRACT FROM AUTHOR]

Slope stability models traditionally use simple indicators of root system structure and strength when vegetation is included as a factor. However, additional root system traits should be considered when managing vegetated slopes to avoid shallow substrate mass movement. Traits including root distribution, length, orientation and diameter are recognized as influencing soil fixation, but do not consider the spatial and temporal dimensions of roots within a system. Thick roots act like soil nails on slopes and the spatial position of these thick roots determines the arrangement of the associated thin roots. Thin roots act in tension during failure on slopes and if they traverse the potential shear zone, provide a major contribution in protecting against landslides. We discuss how root traits change depending on ontogeny and climate, how traits are affected by the local soil environment and the types of plastic responses expressed by the plant. How a landslide engineer can use this information when considering slope stability and management strategies is discussed, along with perspectives for future research. This review encompasses many ideas, data and concepts presented at the Second International Conference ‘Ground Bio- and Eco-engineering: The Use of Vegetation to Improve Slope Stability—ICGBE2’ held at Beijing, China, 14–18 July 2008. Several papers from this conference are published in this edition of Plant and Soil. [ABSTRACT FROM AUTHOR]

Scarcity of water causes a shift from flooded to aerobic conditions for rice production in zinc deficient areas in Northern China. This shift alters soil conditions that affect zinc availability to the crop. This paper concerns the effect of aerobic compared to flooded conditions on crop biomass production, grain yield and zinc content. A field experiment was done with six rice genotypes ( Oryza sativa L.) grown on a calcareous soil, both with (23 kg Zn ha−1) and without Zn fertilization. Sampling was conducted at tillering and physiological mature stage. Zn concentration in the shoots was significantly lower at both stages in plants grown in the aerobic field. At maturity, Zn uptake, biomass production, grain yield and Zn-harvest index [grain Zn/(shoot + grain Zn)] were lower under aerobic cultivation. Rice genotypes including aerobic rice and lowland rice differ in degree of response to low Zn supply. A twofold difference was found among aerobic genotypes in grain yield and Zn uptake. Also Zn-harvest index varied significantly. Zn application affected neither grain yield nor grain Zn content, although it significantly improved biomass production in both systems in most genotypes. These results demonstrate that introduction of aerobic rice systems on calcareous soils may increase Zn deficiency problems. [ABSTRACT FROM AUTHOR]

A comparison of structure and pattern of the soil seed bank was made between active and stabilized sand dunes in northeastern Inner Mongolia, China. The objective of this paper was to determine the significance of seed bank in vegetation restoration of sand dunes. The results showed that (1) average seed density decreased from stabilized sand dune to interdune lowland of stabilized sand dune, to interdune lowland of active sand dune, and to active sand dune; (2) horizontally, along the transect from interdune lowland to ecotone and to sand dune top, a ‘V’ shaped pattern was presented in the active dune system, and a reverse ‘V’ shaped pattern in the stabilized sand dune system; (3) vertically, the proportion (accounting for the total seeds) of seeds found in 0–20 mm soil profile decreased from stabilized sand dune to interdune lowland of stabilized sand dune, to interdune lowland of active sand dune, and to active sand dune. The same order was also found in 20–50 mm and 50–100 mm soil profiles; (4) the Sokal and Sneath similarity indices in the species-composition between soil seed bank and above-ground vegetation were ranked as: the stabilized sand dune (24%) > the interdune lowland of active sand dune (21%) > the interdune lowland of stabilized sand dune (18%) > the active sand dune (5%); and (5) vegetation restoration of active sand dunes depends on the dispersal of seeds from nearby plant communities on the interdune lowlands. Much effort must be made to preserve the lowlands, as lowlands are the most important seed reservoir in the active sand dune field. [ABSTRACT FROM AUTHOR]

Background and aims: Water is fundamental to the growth of plants by participating in plant metabolism, and nutrient transport and maintaining the integrity of the hydraulic system. Knowledge of water use characteristics among co-occurring plant species is crucial for understanding the ecohydrological processes and community assemblages. However, interspecific interactions with respect to water sources and physiological activity remain poorly understood. Methods: The stable oxygen isotope values of xylem and soil water, and leaf physiological characteristics were measured in three communities in the Mu Us Desert, northwest China: a mixed shrub and grasses community; a pure shrub community; and a pure grasses community. Results: In mixed communities, the main water source for shrubs shifted to deeper soil layers than in pure communities, whereas grass water use switched to shallower soil layers. Leaf photosynthetic rates, stomatal conductance, transpiration, and water potential of both species were significantly lower in mixed communities than in pure communities. These results suggest that interspecific interactions influenced plant water use patterns. The water-use efficiency of shrubs increased in mixed communities, whereas that of grasses decreased, indicating that grasses exacerbated water stress on shrubs, while shrubs relieved water stress on grasses. Additionally, leaf physiological activity was positively correlated with shallower water sources and negatively correlated with deeper water sources. Conclusion: Our findings show that plants responded to interspecific interactions under drought conditions through the coupling of plant water sources with leaf physiologies. The present study provides important insights into water-related reforestation and ecological management in dryland ecosystems. [ABSTRACT FROM AUTHOR]

Background: Studying green manure decomposition in various returning methods can establish a scientific foundation for farmland nutrient management. Methods: In a rubber plantation on Hainan Island, China, utilized the nylon mesh bag method to imitate the decomposition of kudzu (whole plant, stem, and leaf) under two returning methods (mulching and burying) in two different sites (young and mature rubber plantations). The study examined the decomposition rate and nutrient release dynamics of kudzu, as well as the effects of kudzu reintroduction on several soil properties including soil pH, soil organic carbon (SOC), total nitrogen (TN), total phosphorus (TP), nitrate nitrogen (NO3−-N), ammonium nitrogen (NH4+-N), available phosphorus (AP), and enzyme activities. Results: Compared with mulching, the burying returning method significantly increased the kudzu decomposition rate and nutrient release proportions. After 270 days, more than 80% of the C, N, and P in different components of kudzu were released. The decomposition rate was found to be more affected by the initial soil factors than by the endogenous nutrients of kudzu. Compared with CK, all kudzu treatments led to significant increases in soil enzyme activities and soil pH, SOC, NO3−-N, and AP concentrations in two rubber plantations. The TN and NH4+-N concentrations were significantly increased in mature rubber plantations, while the TP was the opposite. Conclusion: The kudzu returned can effectively alleviate soil acidic, improve soil nutrient availability, regulating soil enzyme activities of the rubber plantation in the short-term. These results provide a scientific basis for the rational application of kudzu in rubber plantations. [ABSTRACT FROM AUTHOR]

Aims: Vegetation restoration has been widely implemented to achieve carbon (C) sequestration and prevent land degradation, and this study aims to evaluate the ecosystem C pools and C sequestration effectiveness of different land-use types. Methods: In this study, the plant biomass C stock, litter C stock, soil organic C (SOC) stock and ecosystem C sequestration in Zanthoxylum bungeanum plantations (with stand ages of 28, 20, 15 and 8 years, abbreviated as ZB28, ZB20, ZB15 and ZB8, respectively), abandoned land (AL) and farmland (FL) were estimated. Results: (1) the plant biomass and biomass C stock of above-and below-ground increased after farmland conversion, and all of them ranked as ZB28 > ZB20 > ZB15 > AL > ZB8 > FL; (2) the litter stock and C stock, and SOC concentration and stock of different land-use types ranked as AL > Z. bungeanum plantations > FL, and these indices increased with the stand age; (3) the C stock of the ecosystem in FL was 115.4 Mg C ha−1, and the C stock of the ecosystem increased by 8.9–66.6 Mg C ha−1 and 52.4 Mg C ha−1 after the conversion of FL to Z. bungeanum plantations and AL, respectively; (4) and soil C sequestration accounts for 55.6–83.6% of ecosystem C sequestration after farmland conversion. Conclusions: This implies that the conversion of farmland to Z. bungeanum plantations was the best approach in the arid valley area when the ecosystem C sequestration and economic benefits were considered. [ABSTRACT FROM AUTHOR]

Background and aims: Coastal wetland types have been severely altered by human reclamation activities and Spartina alterniflora invasion. However, how these changes impact C-N-P stoichiometry and nutrient allocation of coastal plants remain unclear. Methods: We investigated C, N, and P contents and ratios in leaf, stem, and root from 30 sites with adjacent natural wetlands (as control, dominated by native Phragmites australis), reclaimed wetlands (dominated by native P. australis), and invasive wetlands (dominated by exotic S. alterniflora) across eastern coast of China. Results: C content and N:P ratio remained constant, N and P contents decreased significantly, but C:N and C:P ratios increased with increasing latitude in natural wetlands. While the direction or magnitude of these latitudinal patterns in reclaimed and invasive wetlands were extremely changed at both individual and organ level. Interestingly, leaf had significant higher C, N, and P contents but lower C:N and C:P ratios than stem and root in each wetland. Compared with natural wetlands, both reclaimed and invasive wetlands had significant lower C and N contents and N:P ratio but higher C:N ratio, invasive wetlands also had significant higher leaf P content. P. australis enhanced the homeostasis for N:P, strength allometric relationship of N and P in leaf, but exhibited a isometric relationship of N and P at individual level after reclamation. S. alterniflora had strict homeostasis for N, P and N:P in most organs and strong ability to decouple the allometric relationship of N and P in leaf, and N changed faster than P at individual level. Conclusions: Importantly, large-scale observations showed that reclamation and especially S. alterniflora invasion significantly decreased N:P ratio in each organ, which might highly affect below- and above-ground trophic chains in the future. Our study provides practical insights in understanding species-specific and multiorgan biogeochemical process and the nutrient allocation strategies of plants under reclaimed and invasive pressures in coastal salt marshes. [ABSTRACT FROM AUTHOR]

Background and aims: Phytolith analysis is a promising tool for paleovegetation reconstruction. However, compared with grass phytoliths, there are few studies that have classified the phytoliths of trees. Therefore, reliable definitions of phytolith types in woody plants and studies of representative woody phytoliths in soils are needed to provide an improved basis for reliable phytolith-based vegetation reconstruction. Methods: To explore the morphology of woody phytoliths and their preservation in soils, we described the phytolith morphology of 60 common broadleaved woody plants in the mid-subtropical zone of China, based initially on anatomical origin, and then on shape and finally on texture. We also for the first time established an index (R value) to explore the preservation of broadleaved woody phytoliths in soil in this region. Results: We divided the phytoliths of broadleaved woody plants into 6 major types and 35 sub-types. The 6 major types are: Epidermal Cell, Silicified stomata, Tracheary, Favose, Haircell, and Others. We found some degree of correspondence between different phytolith types and the parent plants. Fagaceae, Lauraceae, Magnoliaceae, Rosaceae, Anacardiaceae and Euphorbiaceae could be clearly distinguished from other families based on phytoliths. Only eight types of broadleaved woody phytoliths were present in the soils. Elongate attenuate, Elongate entire, and Polyhedral were better preserved in soils than the other types (Elongate entire attenuate, Tabular sinuate, Hair, Sclereid, and Favose). Conclusion: Our results provide a more accurate reference for broadleaved wood phytoliths in interpreting paleovegetation in this region. [ABSTRACT FROM AUTHOR]

Background and aims: According to the nitrogen-disease hypothesis, plant diseases will become more serious with the aggravation of global nitrogen (N) deposition. Numerous studies have indicated that Epichloë endophytes can enhance host plant resistance to pathogens. It is unclear how the competitive ability of endophyte-infected (EI) over endophyte-free (EF) plants changes under the interference of N deposition and plant disease. Methods: In this study, Achnatherum sibiricum, native to the Inner Mongolia steppe of China, was used as experimental material. We experimentally manipulated N addition and pathogen inoculation and examined the growth and competition between EI and EF A. sibiricum. Results: The results showed that EI plants had a greater competitive advantage than EF plants under low N conditions, and this advantage decreased with the N supply. When high N and pathogens were both present, pathogen inoculation reversed the adverse effects of high N supply on the competitive advantage of EI A. sibiricum. Epichloë endophytes not only reduced the disease of EI plants but also reduced the disease of neighboring EF plants. Meanwhile, Epichloë endophytes changed the response of the host disease to N. The disease index of EF plants increased with increasing leaf N content, while that of EI plants did not change. Conclusion: This study highlights that under the dual factors of N deposition and pathogen infection, endophytic fungi improve the competitive ability of host plants. Our results show that considering both biotic and abiotic factors is crucial for predicting the dominance of plant-fungal symbionts in the community. [ABSTRACT FROM AUTHOR]

Purpose: Elucidating the interactions of above- and below-ground communities in forest ecosystems is of great importance for comprehending biodiversity maintenance and ecosystem functioning. Methods: In the context of a Biodiversity and Ecosystem Functioning experiment conducted in China (BEF-China), we explored the combined effects of tree species richness (1, 2, and 4) and shrub species richness (0, 2, 4, and 8) on soil fungal community diversity and structure under tree species with different mycorrhizal types (i.e., arbuscular mycorrhizal (AM) tree and ectomycorrhizal (EM) tree) using the Illumina sequencing method. Results: Results demonstrated that the fungal alpha diversity, community composition and network structure were significantly different between EM trees and AM trees. Although tree and shrub species richness had no significant interactive effect on soil fungal alpha diversity regardless of tree mycorrhizal types, however, their interactions did influence fungal community composition and co-occurrence network structure. Specifically, the interactive effect of tree and shrub species richness on soil fungal community composition was observed in AM trees, and their interactions affected the soil fungal co-occurrence network structure in EM trees. Conclusions: These findings highlight the tree mycorrhizal type dependence of the interactive effects of tree and shrub species richness on soil fungal communities in a subtropical forest. [ABSTRACT FROM AUTHOR]

Aims: Elucidating the mechanisms of understory vegetation response to forest management practices is critical to the impact of soil nutrient cycling. However, as common management practices, how thinning leading to the restoration of understory vegetation affects soil biochemical properties and microbial-mediated belowground processes and their main drivers remains unclear. Methods: We investigated the differences of 16 S rRNA, nifH gene abundance, diversity and composition of vegetation restoration using a 5-year in situ experiment including Pinus massoniana-dominated forests (CK), virgin Cunninghamia lanceolata plantations (CF) and C. lanceolata plantations that have undergone a cycle of cutting and replanting (CS) in southern China. Results: We found that understory vegetation restoration improved some soil physicochemical properties (e.g., AP) and enzyme activity. The abundance of nifH were higher in CF than in CK or CS. As a result of vegetation restoration, α-diversity of soil diazotrophic communities significantly increased in CF. These communities were clustered into different groups based on the forest type. The number of potential keystone species of diazotrophs was highest in CF, including several beneficial taxa (e.g., Paraburkholderia and Pelomonas). Most of the bacterial functional groups related to soil nitrogen cycling were also significantly elevated in CF, such as nitrogen fixers. Partial least squares path modelling (PLS-PM) further showed that soil diazotrophic communities were clearly shaped by soil nutrient content. Conclusions: Overall, these results highlight the effects of vegetation restoration on soil diazotrophic communities and clarify the contributions of potential for improving edaphic conditions in areas of southern China with acidic red soils. [ABSTRACT FROM AUTHOR]

Background and aims: Insight for vegetation restoration in karst mountains could come from understanding the methods by which communities are built along a successional chronosequence. We integrated species diversity, phylogenetic structure, and functional trait diversity to investigate the mechanisms governing community assembly along a successional chronosequence in the northern tropical karst mountains, South China. Methods: Five successional sequences, including grassland, shrubland, young forest, middle-aged forest, and primary forest, were selected in the northern tropical karst mountains using the space-for-time substitution method. The relationships between species diversity and environmental variables (elevation, slope degree and rock exposed rate) were investigated using redundancy analysis and variance partitioning methods. Results and discussion: Our results showed that as succession progressed, species and phylogenetic diversity showed an increasing trend, then a decreasing trend, with the maximum value occurring in young forests, which displayed the optimum curves over the successional gradient. In terms of functional diversity, shrubland, and young forest had significantly higher functional richness than grassland and middle-aged forest, and grassland and young forest had significantly higher quadratic entropy coefficients than primary forest. The vegetative community changed in phylogenetic structure from clustering in the early stages of succession to diverging in the late stages.In contrast, the leaf thickness density decreased as succession progressed, suggesting that the young forest vegetation had the highest resource acquisition ability and utilization rate as the successional progressed. Additionally, the chlorophyll content, leaf thickness, and leaf area showed a first increased then decreased trend as successional progressed. Conclusions: Our results suggest that due to harsher soil conditions, the vegetation in early successional stage was dominated by environmental filtering (i.e., limitation of environmental resources), whereas the vegetation in late successional stage was governed by competitive exclusion (i.e., species competition). Our findings can guide plants conservation and ecological restoration in the tropical karst regions. [ABSTRACT FROM AUTHOR]

Background and aims: Potassium (K), Calcium (Ca), and magnesium (Mg) are essential nutrients for plant and animal growth. The ratio of K/(Ca + Mg) in forage is considered as an indicator of grass tetany. While atmospheric nitrogen (N) deposition is declining or projected to decline in many countries, it remains unknown whether historical N inputs would have legacy effects on K, Ca, and Mg nutrition in soil and plants. Methods: After the cessation of 6-yr N addition with wide-ranging rates, we measured the concentrations of K, Ca, and Mg in soil and plants in a temperate steppe of northern China during three successive years from 2016 to 2018. Results: Soil K/(Ca + Mg) ratios were increased by historical N addition across the three years. Soil K/(Ca + Mg) ratios were higher than 0.08, indicating potential occurrence of grass tetany for ruminants. Plant mineral concentrations and K/(Ca + Mg) ratios at the plant community level showed no variation with increasing historical N addition rates in all the three years, except for the increasing K and Ca concentrations in 2017. All plant functional types showed strong stoichiometric homeostasis with respect to nutrient concentrations, which contributed to the stable forage K/(Ca + Mg) ratio under the N-induced increasing soil K/(Ca + Mg) ratio. Conclusion: Our results highlight the critical role of stoichiometric homeostasis in maintaining forage non-N mineral nutrition of natural grasslands under the background of soil nutritional alterations. [ABSTRACT FROM AUTHOR]

Aims: The anthropogenic nitrogen (N) input has considerable consequences on soil microbial biomass, which is critical for biogeochemical cycling. As prevalent grassland management, mowing may reduce soil N storage, enhance plant biodiversity and soil microbial carbon (C) availability, all of which are important regulators of soil microbial biomass. However, convincing data is still scarce about how mowing affects soil microbial biomass under N enrichment. Methods: The interactive effects of N addition (0 – 50 g N m−2 yr−1) and mowing (unmown vs. mown) on soil microbial biomass C (MBC) were measured by manipulating 6 years' N addition experiment in Inner Mongolia grassland of China. Results: Mowing increased soil inorganic N concentration, available Cu2+ concentration, plant aboveground net primary production (ANPP), species richness, Shannon-Wiener biodiversity and ratio of fungal to bacterial biomass, and decreased soil available Mn2+ concentration under N enrichment. Mowing also significantly reduced the dominance of Leymus chinensis. While mowing did not affect the soil MBC compared with that in only N added plots. The soil MBC was positively regulated by plant species richness and biodiversity, while was negatively regulated by ANPP, soil inorganic N, available Cu2+ and Mn2+ concentration in mown plots. Conclusions: The results highlight that mowing cannot mitigate the negative effects of N enrichment on soil MBC. The soil, plant and microbial properties play important roles in regulating the response of soil MBC to mowing in N-enriched soil. This work improves the mechanistic understanding of the linkages between plant community and soil microbial C cycling. [ABSTRACT FROM AUTHOR]

Purpose: Carbohydrate-active enzymes (CAZymes) mediate carbohydrate turnover and play vital roles in plant- and microbial-derived carbon decomposition. However, the changes of genes that encoding enzymes for plant- and microbial-derived carbon decomposition along environmental gradients remains unclear. Methods: We used metagenomic sequencing to explore changes in genes encoding enzymes for carbon decomposition in five forest sites along an elevational gradient (1503–3182 m) on Qinling Mountain, China. Results: The genes encoding CAZymes showed various patterns along the elevational gradient. In particular, the abundance of genes encoding auxiliary enzymes and glycoside hydrolases decreased with increasing elevation. The abundance of genes encoding enzymes for plant- and fungi-derived carbon decomposition was higher at low elevations than at high elevations, whereas the abundance of genes encoding enzymes for bacteria-derived carbon decomposition was higher at high elevations than at low elevations. The results indicate contrasting patterns of fungal- and bacterial-derived carbon decomposition with elevation. Proteobacteria and Acidobacteria were the dominant species that decomposed dead plant and microbial biomass. Moreover, our results reveal that soil properties (i.e., ammonium nitrogen and bulk density) and vegetation properties dominated the CAZymes gene distribution along the elevational gradient. Conclusion: Bacteria- and fungi-derived carbon decomposition potentials show contrasting elevational patterns in forest soils; soil and vegetation properties are common controls for the elevational patterns. [ABSTRACT FROM AUTHOR]

Background and aims : N nutrition index (NNI) diagnosis and N requirement (Nfr) estimation are essential for accurate N management in the fertirrigation system. However, the NNI after straw retention and the relationships between NNI, Nfr, and relative yield (RY) are all not fully understood. Methods: A three years field trial with three straw incorporation methods (without straw (NI), with straw (SI), and straw-derived biochar incorporation (BI)) and five N rates (0, 150, 225, 300, and 375 kg ha−1) was conducted on drip-irrigated maize in northwest China. Soil NO3−-N content (CN), N recovery efficiency (REN), NNI, Nfr, and grain yield under NI, SI, and BI were compared. Later, the mathematical relationships between NNI, Nfr, and RY were defined. Results: Results showed that compared with NI, the N input during the reproductive stage could be reduced under SI and BI to achieve higher grain yield with NNI increased due to an increase in CN. In addition, Nfr was calculated by dividing N accumulation deficit (NAD) by REN, where a significant linear relationship existed between NAD and NNI (NAD = S(1-NNI)), and the slope of the NAD-NNI regression (S) varied quadratically with days after sowing (DAS). NNI and RY were also related in linear plus plateau functions, and the maximum RY was achieved when NNI was 0.88. Conclusions: Based on patterns of variance, three easily accessible independent variables (DAS, REN, and NNI) were used to create and verify Nfr estimating techniques for generating higher yields in maize under NI, SI, and BI. [ABSTRACT FROM AUTHOR]

Purpose: As a huge natural carbon storage, wetlands play an important role in the global carbon cycle. However, the spatial pattern and storage of soil organic carbon (SOC) in wetland ecosystems remain largely uncertain due to large spatial heterogeneity and insufficient field observations. Methods: In this study, we predict the spatial pattern of SOC density and estimated SOC storage in wetlands of Northeast China based on 819 field samples and multiple geospatial data using random forest algorithm. Results: The SOC density of wetlands at different depths was affected differently by environmental factors and the SOC density in the surface layer (0–30 cm) was more susceptible to climatic change. The correlation coefficients (r) between the SOC density predicted by the random forest model and the measured SOC density were 0.86, 0.77 and 0.73 in 0–30, 30–60 and 60–100 cm soil depths, respectively. Our estimation showed that Northeast China holds huge wetland SOC storage in the amount of 3.40 ± 0.13 Pg C. The average wetland SOC density was 44.30 ± 1.72 kg C m−2, which decreased gradually from north to south in the study area. Conclusion: The wetland SOC density in Northeast China decreased with soil depth, and the influence of environmental factors on wetland SOC gradually decreased. Surface wetland SOC may be more sensitive to global climate change. Our results examined the relationship between wetland SOC and environmental factors, which benefits the understanding of the responses of wetland SOC to climate change. [ABSTRACT FROM AUTHOR]

Aims: Soil phosphorus (P) cycling in karst regions is mainly regulated by microbial activities. Natural restoration has been widely adopted in the degraded karst regions of southwest China. However, the response of functional genes and microbial communities involved in soil P cycling to revegetation has not been well characterized. Methods: We used metagenomic sequencing to investigate the genes and microorganisms related to soil P cycling derived from natural restoration stages (shrubbery, TG; secondary forest, SG; old-growth forest, OG) in the southeast of Guizhou Province, China. Results: Natural restoration affected the composition of soil P cycling genes. When TG restored into OG, the relative abundance of organic P (OP) mineralization genes increased from 45.78% to 48.38%, while the genes related to inorganic P (IP) solubilization decreased from 27.19% to 25.03%. The effect of soil nutrients on the relative abundance of OP and IP genes was greater than that of aboveground plant diversity. Structural equation modeling further indicated that soil nutrients directly drove the increase in the relative abundance of OP genes and indirectly impacted the relative abundance of IP genes. The results show that Proteobacteria (38.97%–52.72%) and Actinobacteria (13.44%–29.34%) are the main contributors to soil OP and IP cycling genes, but their contributions vary in different restoration stages. Conclusions: Natural restoration of the degraded karst vegetation changes the acquisition strategy of soil microbial P by enhancing OP but decreasing IP cycling potentials. This study investigate the regulation of P cycling in the ecological restoration of degraded karst regions from microbial perspective. [ABSTRACT FROM AUTHOR]

Aims: It is essential to explore tree root development, dynamics and its control factors to improve the productivity of plantations. Tree provenance and soil lithology may jointly regulate root growth in subtropical plantations, but this relationship has not yet been quantified. Methods: We used a split-plot design with tree provenances (DY, GP, CY, SG, TM) and soil lithology (basalt, quartz sandstone, feldspathic quartz sandstone, blastopsammite) to determine the root growth of 4-year-old Masson pine seedlings in combination. Results: Our results showed an interaction effect between tree provenances and soil lithology on root surface area (RSA), root length (RL), root volume (RV), root biomass (RB), specific root surface area (SRA) and specific root length (SRL). The RV, RSA, RL, RB, and SRL of the DY provenance were higher than those of the other provenances due to site conditions similar to the planting site (e.g., climate, altitude, and latitude); the RSA, RV, SRL, SRA and RB of DY provenance on the soil with lithology of blastopsammite were significantly lower than those of feldspar quartz sandstone and quartz sandstone, which indicates that the root growth is also affected by soil lithology. Furthermore, soil bulk density, total soil potassium, soil organic carbon and soil particle composition were the main factors affecting root growth in basalt, quartz sandstone, feldspathic quartz sandstone and blastopsammite soil, respectively, indicating that the required soil properties by plants changes with changes in the soil environment. Conclusions: We conclude that provenance and soil lithology jointly drive the root growth of young subtropical plantations. [ABSTRACT FROM AUTHOR]

Aims: The inhomogeneity of bare rock distribution and the diversity of underground rock structure in different soil-rock microsites resulted in high soil heterogeneity. The aim of this study was to investigate the responses of soil nutrients and stoichiometry to soil-rock microsites and evaluate the relationship between soil substrate and SOC stability Methods: Six soil-rock microsite types were selected in a karst area of Southwest China, including rocky soil surface (RSS), stone crevice (SC), stone gully (SG), stone cave (SCA), stone pit (SP) and soil surface (SS). Soil samples were collected from 0–10, 10–20 and 20–30 cm depths, and three carbon fractions were isolated by combining flotation and screening. Results: The stocks of carbon (C), nitrogen (N), phosphorus (P) and sulfur (S) in the soil profile among different soil-rock microsites were in the order of SS > RSS > SG > SC > SCA > SP. SCA and SS contained the highest and lowest values of C, N, P and S densities, respectively. The N, P and S were positively correlated with LF/SOC and negatively with MF/SOC, stoichiometric ratios were also negatively with MF/SOC. Moreover, the saturation moisture content, capillary moisture capacity, and saturated hydraulic conductivity are important indicators that affect the SOC stability. Conclusions: These results imply that soil-rock microsites regulate the stability of SOC by affecting the heterogeneity of soil nutrients and water, and the retention of soil water modulates the effects of soil nutrients and stoichiometry on the stability of SOC in karst areas. [ABSTRACT FROM AUTHOR]

Aims: As the largest terrestrial carbon (C) pool, soil organic carbon (SOC) plays a critical role in the global C cycle. Particulate organic carbon (POC) and mineral-associated organic carbon (MAOC) are currently popular methods for the fractionation and analysis of SOC. Nitrogen (N) addition affects SOC dynamics. However, the characteristics of POC and MAOC and their potential drivers under N (inorganic and organic N) addition remain unclear. Methods: We conducted a meta-analysis based on data from 50 studies on terrestrial ecosystems in China to investigate the responses of SOC, POC, and MAOC to N addition, and to reveal the factors influencing POC and MAOC. Results: The results showed that organic N addition significantly increased the SOC (effect size: 0.35), POC (effect size: 0.68), and MAOC (effect size: 0.20), whereas inorganic N addition significantly increased SOC (effect size: 0.10) and POC (effect size: 0.21). POC and MAOC concentrations increased with fertilization duration (years); however, the physical stability of SOC remained unchanged. No correlation was observed between the SOC sequestration rate and duration of fertilization under inorganic N addition, whereas the SOC sequestration rate showed a trend of first increasing and then decreasing with organic N addition. Conclusions: The main factors affecting POC and MAOC were microbial biomass carbon (MBC) and soil pH, and the driving factors of POC and MAOC were different under inorganic and organic N additions. Additionally, N addition may decrease the stability of the SOC pool. [ABSTRACT FROM AUTHOR]

Aims: Conversion from pure plantations to mixed plantations can significantly increase forest productivity and provide better ecosystem services, yet there is still a lack effective of assessment methods to determine how this conversion affects belowground biodiversity and ecological functions. Methods: We conducted an in-situ experiment to investigate the impacts of forest conversion (Cunninghamia lanceolata pure plantations vs. C. lanceolata-Betula luminifera mixed plantations) on soil multifunctionality, bacterial composition, network patterns and assembly mechanisms in southern subtropical China. Results: The results showed that compared with monoculture plantations, most soil physicochemical properties and enzyme activities were higher in mixed plantations. The mixed plantations increased bacterial α-diversity, and community structure differed between the two forest types. Network analysis showed that the network structure of the mixed plantation was more complex and stable, and contained more keystone taxa. Furthermore, stochastic processes primarily governed the assembly of bacterial communities. Forest conversion increased habitat niche breadth and the importance of stochastic processes. Based on PICRUSt2, the mixed plantations significantly increased soil multifunctionality and bacterial functions (e.g., carbohydrate metabolism and energy metabolism). Moreover, variations in the bacterial community and functionality were highly correlated with soil pH and nutrients. Conclusions: Our study showed that the conversion of monoculture plantations into mixed plantations enhances soil fertility and has more positive benefits. The changes in soil bacterial composition and function were mainly mediated by soil pH and nutrient increases caused by forest conversion, which contributes to assessing the eco-environmental effects of mixed planting in reforestation. [ABSTRACT FROM AUTHOR]

Purpose: We sought to identify the effects of elevationally (1560−2160 m) driven climate (mean annual air temperatures of + 4.0 to + 10 oC and mean annual precipitation of 900–1200 mm), forest type and soil property variations on soil greenhouse gas (GHG) fluxes in the Qinling Mountains, China. Methods: Soil GHGs were monitored at five temperate forest sites using static chambers for two full years. The related edaphoclimatic parameters were also monitored. Results: The cumulative soil CO2 and N2O emissions and the CH4 uptake from the five sites ranged between 3.82 to 7.48 t CO2-C ha−1 yr−1, 1.19 to 2.25 kg N2O-N ha−1 yr−1, and 0.89 to 5.67 kg CH4-C ha−1 year−1, respectively. Average soil CO2 emissions decreased with increasing site elevation, whereas CH4 and N2O fluxes showed no clear relationship with site elevation. All sites were net CH4 sinks. Occasionally, soils switched to net sources of CH4 during summer or autumn rainfall events at all sites. All sites were net N2O sources although short periods of soil N2O uptake were observed during freeze–thaw cycles and during summer rainfall. The source strength of N2O and CH4 differed during summer and winter and snowfall which had direct effects on soil water content. Conclusions: Site elevation could be used as a predictive variable for constructing regional soil CO2 emissions budgets, whereas soil CH4 and N2O fluxes are driven by a more complex interplay of climatic and soil biochemical variables, which are more difficult to integrate on a regional scale. [ABSTRACT FROM AUTHOR]

Aim: Phosphorus (P) is vital for ecosystem functioning, but how boreal forest succession affects soil P is not yet well defined. Method: We collected 134 soil samples from ten plant succession stages of climax vegetation of larch forests in the Greater Khingan Mts., northeast China, and measured soil total P (TP) and nine fraction-Ps, together with detailed records of trees, shrubs, herbs diversity, and geo-topographical conditions. Results: Our results showed that TP and nine fraction-Ps declined non-linearly in the chronosequence in concentration, and three organic fractions (NaHCO3-Po, NaOH-Po, and conc.HCl-Po) showed a similar non-linear decrease. The stoichiometric percent of Pi, conc.HCl-Pi and NaOH-Pi linearly increased (R2 = 0.81–0.92), and Po, NaOH-Po, and Re-P decreased linearly (R2 = 0.59–0.61). Partial ordination excluding geo-climatic impacts (30.8%) could identify the exact association between plant succession and P changes. The negative relations between tree diversity, biomass and organic fraction-Ps showed that P storage in tree biomass was responsible for soil P declines during plant succession, and tree diversity accelerated these P changes. In contrast, the significantly higher soil P in the grass stage was due to P's grass-upload function to surface soils. Conclusion: Our data highlighted that soil P was depleted, with a higher Pi proportion during plant succession in high-latitude boreal forests, favoring precise soil P management and evaluation of these forests. [ABSTRACT FROM AUTHOR]

Background and aims: Sea-buckthorn (Hippophae rhamnoides) is widely domesticated and cultivated in orchards worldwide. With the advantages of a large root system and the symbiosis of fibrous roots with Frankia, a group of N2 fixing bacteria which form nodules with the roots, sea-buckthorn can grow in harsh environment under extreme weather conditions. However, its tolerance to petroleum contamination in the soil has so far not been studied. To elucidate whether sea-buckthorn can be employed for phytoremediation of petroleum contamination, its remediation efficiency as well as its growth and metabolic traits in petroleum contaminated soil were examined in an experiment with potted plants. Methods: Sea-buckthorn seedlings were planted in soils with four different petroleum concentrations from April to September in a pot experiment. The responses of growth, gas exchange and the antioxidative system were examined on three sampling dates. After 5.5-month of exposure, soil petroleum remediation was evaluated in planted and unplanted soils. Results: The petroleum decontamination rate was significantly enhanced by H. rhamnoides in soils with petroleum contamination up to 15 g kg−1 after one growing season. The root to shoot ratio increased continuously with the increase of the petroleum concentration as a consequence of reduced biomass allocated to the shoots, probably as a mechanism to counteract stress by the petroleum contamination of the soil. Photosynthesis was enhanced by lower petroleum concentrations in the soil (≦15 g kg−1) in September. Short-term exposure (in July) to high petroleum concentrations (20 g kg−1) in the soil enhanced ascorbate peroxidase (APX), glutathione reductase (GR), superoxide dismutase (SOD), and catalase (CAT) activity and increased ascorbic acid (AsA) and glutathione (GSH) contents, indicating elevated activity of the Foyer-Haliwell-Asada-Cycle. However, similar effects were not observed at long-term exposure. Conclusions: Our results prove that sea-buckthorn is a promising tool for phytoremediation of petroleum contaminated soils up to 15 g kg−1 in loess plateau soil in China. [ABSTRACT FROM AUTHOR]

Background and Aims: Soil net nitrogen mineralization (Nmin) rate and its temperature sensitivity (Q10) are critical parameters for predicting nitrogen availability under global warming. However, the controlling factors of the net Nmin rate and its Q10 at the regional scale remain highly uncertain, especially in different ecosystem types. Methods: An incubation experiment at three different temperatures was conducted to measure the net Nmin rate and to calculate its Q10. High-throughput sequencing was applied to explore the microbial community diversity and composition. Results: Results showed that the overall net Nmin rate was highest in paddy fields, followed by forest and dryland fields, whereas its Q10 was not different among ecosystems. Structural equation models revealed that the net Nmin rate was mainly affected by soil properties in dryland habitats, whereas it was mainly influenced by soil microbial communities and mean annual temperature (MAT) in paddy habitats. In forest habitats, the net Nmin rate was mainly affected by bacterial communities rather than fungal communities. The Q10 of net Nmin was close to 2.0, indicating that the net Nmin rate is sensitive to climatic warming. The Q10 was impacted by the bacterial community composition in dryland soils, whereas it was influenced by soil properties and bacterial diversity in paddy and forest soils. Conclusion: This study provides a novel quantification on the contribution of soil microbial diversity and community composition to soil net Nmin process in three ecosystem types, with implications for microbial-mediated N mineralization process under climatic change scenarios. [ABSTRACT FROM AUTHOR]

Aims: Ecological stoichiometry plays an important role in biogeochemical cycles and ecosystem functions. However, we know little of fine-root stoichiometry responses to nitrogen (N) addition and whether the responses are similar to those of leaves. Methods: We conducted a field experiment to explore the effects of N addition on carbon: N: phosphorus (C:N:P) stoichiometric ratios and homeostasis in green leaves, fine roots and soil as well as the regulatory effects of plant and soil stoichiometric ratios on forest growth in poplar plantations on the eastern Chinese coast. Results: We found that N addition increased soil organic C (SOC), soil available N and P, and soil N:P and decreased soil C:N. We also found that N addition increased leaf C and N, N:P and C:P of green leaves and fine roots, while it decreased fine root C and P as well as green leaf and fine root C:N. The consistent responses of green leaf and fine root stoichiometry to N addition were attributed to stoichiometric homeostasis. That diameter at breast height (DBH) and fine root biomass (FRB) growth contradicted C:N:P stoichiometry appeared to be because of their different nutrient uptake and utilization efficiencies. Conclusions: The C:N:P stoichiometry of green leaves and fine roots was generally consistent in response to N addition. These findings contribute to our understanding of the biogeochemical cycles of plantation ecosystems and provide basic data for plantation cultivation and management. [ABSTRACT FROM AUTHOR]

Aims: Interactions among plants are the main biotic driver for the development of spatial vegetation patterns in dryland ecosystems. The modification of soil properties by perennial plants is an important mechanism. We aimed to examine how spatial vegetation patterns were affected by the local changes in soil physiochemical properties beneath shrubs in different communities. Methods: We investigated 36 plots containing shrub vegetation on the Alxa Plateau, northwestern China. Patch sizes of all shrubs were measured. The median and curvature of patch size distribution (obtained by quadratic regression) were selected as indicators for spatial patterns. We determined soil physiochemical properties beneath the canopy of dominant and other shrub species and in adjacent intershrub spaces. A multi-model inference procedure was employed to analyze the standardized effect of the changes in soil properties and their interactions on the spatial vegetation patterns. Results: Local changes in soil physiochemical properties associated with shrub-soil feedbacks affected spatial vegetation patterns in different aspects. Salt aggregation was positively correlated with deviations from the power-law distribution, while nutrient concentration had no significant effect. Interaction between nutrient and salinity concentration positively affected the median patch size, maintaining a stable Turing-like pattern. Heterogeneity analysis showed that the dominant shrub species are representative of plant-soil interactions for the entire community. Conclusions: Our study suggests that soil salinity accumulated under the canopy of shrubs is the key soil property driving the spatial pattern of vegetation patches on the Alta Plateau. [ABSTRACT FROM AUTHOR]

Aims: Soil conditions are one of the most important selection pressures driving local adaptation of plants. Unfortunately, little attention has been paid to soil-mediated local adaptation in early stages of grass species. Thus, soil-mediated local adaptation in early-life stages of Stipa breviflora was investigated in this study. Methods: Here, we collected seed and soil samples from 6 populations spanning almost the entire latitudinal range of S. breviflora in China. Then, the seeds of each population were sown in soils from 6 sites separately. Finally, we analyzed physicochemical and microbial properties of the 6 soils. Results: Home soils significantly enhanced seed germination of population A, B and C, while not for population D, E and F. For field seedling emergence, only population E and F were observed that the seedlings planted in home soils were higher than those planted in non-home soils. However, seedling survival of population A, B, C and F planted in home soils was higher than those in non-home soils. No significant difference in seedling overwintering was observed between populations planted in home soils and those planted in non-home soils. Moreover, the structural equation modeling (SEM) suggested that soil traits indirectly affected seedling survival by mainly altering soil fungal diversity and total nitrogen concentration. Conclusions: These results indicated that soil-mediated local adaptation exists in early-life stages of S. breviflora, while its strength of local adaptation varies across populations and early development stages. These findings provide new insights into the role of soil conditions in local adaption of plants. [ABSTRACT FROM AUTHOR]

Purpose: It has always been challenged to improve heavy coastal silt saline soil for crop productions through establishing an irrigation system with saline water. This study was aimed to investigate the effect of the electricity conductivity of irrigation water (ECw) on soil salinity (ECe), sodium adsorption ratio (SAR) and pH of the saturated paste (pHs), tomato yield, and irrigation water use efficiency (IWUE). Methods: A two-year field experiment of five ECw treatments (0.7, 3.2, 4.7, 6.2, and 7.8 dS m−1, respectively) was conducted under ridge tillage in the Bohai Rim region, China through a drip irrigation system. Results: A linear correlation between ECw and soil desalinization rate (SDR) and between the irrigated water amount and SDR was revealed and the final average ECe, SAR and pHs readings at 1 m deep soil (40.2 dS m−1, 56.2 (mmol L−1)0.5, and 7.82, respectively) dropped to those within the main root zone with each of five treatments (21.3–26.6 dS m−1, to 32.4–37.1 (mmol L−1)0.5 and 7.16–7.75, respectively), indicating an outstanding soil reclamation. The tomato survival rate was over 90% when the ECw was kept below 7.8 dS m−1, while growth and yield of tomato and IWUE were generally unaffected as the ECw was below 4.7 dS m−1. Conclusion: The ECw of dripping water should be maintained below 3.9 dS m−1 and the soil matrix potential be controlled above -5 kPa at 20 cm deep soil beneath dripping emitters for a high-yield tomato cultivation in the heavy coastal silt saline lands. [ABSTRACT FROM AUTHOR]

Purpose: Understanding the interactions among soil microbial communities, soil multifunctionality, and soil-borne pathogens are important for ecological prevention and control of soil-borne diseases. In this study, we aimed to compare the differences in microbial communities and multifunctionality between healthy and Alternaria solani-infected potato rhizosphere soils. Additionally, we investigated the relationships among soil microbial communities, soil multifunctionality, and potato early blight incidence. Methods: We collected healthy and Alternaria solani-infected potato rhizosphere soil samples from a potato field in Ningbo, Zhejiang, China. Amplicon sequencing was used to detect changes in soil microbial communities. The Z scores (standard scores) of soil chemical properties, soil enzyme activities, and potato yield were averaged to obtain soil multifunctionality. Results: We found significantly reduced potato yield, soil multifunctionality, and bacterial richness under diseased conditions. Additionally, there were significant differences between healthy and diseased rhizosphere soil microbial communities. Specific microbial taxa including Kaistobacter, Candidatus Koribacter, Candidatus Solibacter, Rhodoplanes, Bradyrhizobium, Gynumella, Massilia, Alicyclobacillus, Mycochlamys, and Conocybe were enriched in diseased rhizosphere soils. The complexity of microbial co-occurrence networks decreased. The proportion of positive correlations among microbial taxa decreased, whereas the proportion of negative correlations increased in diseased rhizosphere soils. These changes were strongly associated with decreased soil multifunctionality. Conclusion: Our results increased our comprehension of the interactions among soil microbial communities, multifunctionality, and potato early blight, thus providing important implications for the design and implementation of control strategies against soil-borne diseases in the future. [ABSTRACT FROM AUTHOR]

Purpose: Conducting research about the metal accumulation process of wetland plants and relevant rhizosphere mechanism can help better understand the biogeochemical behavior of metals in riparian wetland. However, little relative information is available for riparian wetland. Methods: In this study, we explored the copper accumulation process of dominant plant of Artemisia and rhizosphere mechanism under different water conditions (flooding condition [FC], dry condition [DC] and alternate dry and flooding condition [DFC]) in riparian wetland of Poyang Lake. Results: The results indicated that continuous or intermittent flooding may impede the accumulation and transformation of Cu by Artemisia. The correlation and multivariate analysis indicated that rhizosphere pH, Cu fraction and iron plaque on root surface can significantly influence Cu accumulation process. The transformation of exchangeable fraction to carbonate bound fraction and organic fraction under DFC and FC treatments of Cu may impede its accumulation in Artemisia. Formation of iron plaque under DFC and DC treatments can enhance the Cu accumulation in roots, but impede the translocation of Cu to aboveground tissues. Higher rhizosphere pH under DFC and FC treatments may impede the translocation of Cu by enhancing formation of iron plaque. Additionally, the translocation factor and root/aerial Cu content indicated that Artemisia has the potential for phytoextracting Cu, but the significant decrease of its biomass with Cu addition indicated that Artemisia is not suitable for phytoextracting Cu polluted soil, especially under DFC and FC treatment. Conclusion: DFC and FC treatments can significantly impede the Cu accumulation processes and ability by changing rhizosphere characteristics and decreasing plant growth. [ABSTRACT FROM AUTHOR]