Soil moisture decline in China's monsoon loess critical zone: More a result of land-use conversion than climate change.

Soil moisture (SM) is essential for sustaining services from Earth's critical zone, a thin-living skin spanning from the canopy to groundwater. In the Anthropocene epoch, intensive afforestation has remarkably contributed to global greening and certain service improvements, often at the cost of reduced SM. However, attributing the response of SM in deep soil to such human activities is a great challenge because of the scarcity of long-term observations. Here, we present a 37 y (1985 to 2021) analysis of SM dynamics at two scales across China's monsoon loess critical zone. Site-scale data indicate that land-use conversion from arable cropland to forest/grassland caused an 18% increase in SM deficit over 0 to 18 m depth (P < 0.01). Importantly, this SM deficit intensified over time, despite limited climate change influence. Across the Loess Plateau, SM storage in 0 to 10 m layer exhibited a significant decreasing trend from 1985 to 2021, with a turning point in 1999 when starting afforestation. Compared with SM storage before 1999, the relative contributions of climate change and afforestation to SM decline after 1999 were -8% and 108%, respectively. This emphasizes the pronounced impacts of intensifying land-use conversions as the principal catalyst of SM decline. Such a decline shifts 18% of total area into an at-risk status, mainly in the semiarid region, thereby threatening SM security. To mitigate this risk, future land management policies should acknowledge the crucial role of intensifying land-use conversions and their interplay with climate change. This is imperative to ensure SM security and sustain critical zone services.

Tracing the Sources and Fate of NO3- in the Vadose Zone-Groundwater System of a Thousand-Year-Cultivated Region.

Excess nitrate (NO3-) loading in terrestrial and aquatic ecosystems can result in critical environmental and health issues. NO3--rich groundwater has been recorded in the Guanzhong Plain in the Yellow River Basin of China for over 1000 years. To assess the sources and fate of NO3- in the vadose zone and groundwater, numerous samples were collected via borehole drilling and field surveys, followed by analysis and stable NO3- isotope quantification. The results demonstrated that the NO3- concentration in 38% of the groundwater samples exceeded the limit set by the World Health Organization. The total NO3- stock in the 0-10 m soil profile of the orchards was 3.7 times higher than that of the croplands, suggesting that the cropland-to-orchard transition aggravated NO3- accumulation in the deep vadose zone. Based on a Bayesian mixing model applied to stable NO3- isotopes (δ15N and δ18O), NO3- accumulation in the vadose zone was predominantly from manure and sewage N (MN, 27-54%), soil N (SN, 0-64%), and chemical N fertilizer (FN, 4-46%). MN was, by far, the greatest contributor to groundwater NO3- (58-82%). The results also indicated that groundwater NO3- was mainly associated with the soil and hydrogeochemical characteristics, whereas no relationship with modern agricultural activities was observed, likely due to the time delay in the thick vadose zone. The estimated residence time of NO3- in the vadose zone varied from decades to centuries; however, NO3- might reach the aquifer in the near future in areas with recent FN loading, especially those under cropland-to-orchard transition or where the vadose zone is relatively thin. This study suggests that future agricultural land-use transitions from croplands to orchards should be promoted with caution in areas with shallow vadose zones and coarse soil texture.

Characterization and phylogenetic evolution of mitochondrial genome in Tibetan chicken.

The objective of this study was to characterize mitochondrial genome and investigate phylogenetic evolution in Tibetan chicken. In this study, four haplotypes were identified based on D-loop sequencing in Tibetan chicken (n = 40), and each representative of four haplotypes was selected for total mitochondrial genome sequencing and analyzed together with published mitochondrial genome data of red jungle fowl. Four haplotypes belonged to three previously published clades, i.e., Clade A, clade B and clade E. Based on D-loop sequencing data, the average haplotype diversity and nucleotide diversity were 0.658 ± 0.065 and 0.00442 ± 0.00094, respectively. The mitochondrial genome of Tibetan chicken is 16,785 bp in size, consisting of 22 transfer RNA (tRNA) genes, two ribosomal RNA (rRNA) genes, 13 protein-coding genes and one non-coding control region (CR). Compared with the mitochondrial genome, a phylogenetic tree based on the D-loop sequence had a messy distribution, and no breed cluster pattern was observed in Tibetan chicken. The results indicate that Tibetan chicken populations in our study have relatively low nucleotide and haplotype diversity and likely share multiple maternal lineages. The D-loop sequence has limited power for the resolution of phylogenetic relationships in comparison with the complete mitochondrial genome.

Distribution characteristics and controls of soil organic carbon at different spatial scales in China's Loess Plateau.

Understanding the variations and controls of soil organic carbon (SOC) at different spatial scales can help in selecting edaphic and environmental covariates that enables us to model SOC more accurately. The present study investigated the distribution characteristics and controls of SOC content at various spatial scales, including a deep soil core (204.5 m) taken from land surface down to bedrock (plot scale), two toposequences with different slope aspects (slope scale), and eighty-six soil profiles along a north-south transect under different land uses (regional scale) in China's Loess Plateau. The results showed that SOC content at different spatial scales decreased exponentially with increasing soil depth, but the rate of reduction differed at various spatial scales and in soil layers at different depths. For the deep soil core, the SOC content and the average rate of reduction with depth in the 0-15.5 m soil layer were significantly higher than the corresponding values of the 15.5-34.5 m and 34.5-204.5 m soil layers (p < 0.05). For the toposequences with varying slope aspects, SOC content in the 0-50 cm soil layer declined rapidly with increasing depth; while SOC content in the 50-200 cm soil layer showed relatively no change. There was no significant difference of average SOC content at depths of 0-200 cm for forestland and grassland considering slope aspects that differed or were the same (p > 0.05) due to the similar climatic conditions. However, SOC content within 0-500 cm soil profile under different land uses along the north-south transect exhibited a significant difference (p < 0.05), following the order of farmland (4.94 ± 1.23 g kg-1) > forestland (3.01 ± 1.45 g kg-1) > grassland (2.03 ± 0.68 g kg-1); moreover, the mean SOC content of the 0-500 cm soil profile generally decreased from south to north following the decreasing rainfall and temperature gradient. The average rates of reduction of SOC content in the 0-50 cm soil layer under different land uses (0.0807-0.1756 g kg-1 cm-1) were higher than the values of the 50-200 cm (0.0021-0.0154 g kg-1 cm-1) and 200-500 cm soil layers (0.0001-0.0017 g kg-1 cm-). The SOC content at the plot scale at different depths positively correlated with total nitrogen content. The SOC content at the slope scale was mainly affected by soil water content and saturated hydraulic conductivity, while that at the regional scale was impacted by climate, topography and soil water/clay content. Pedotransfer functions were applied to adequately simulate and predict SOC content at different spatial scales in the studied area, which could provide a foundation to build SOC prediction models and extrapolate the various spatial scales to other loess regions worldwide. Our findings demonstrate the importance of considering the scale effects for efficiently predicting the spatial patterns of SOC and can help in devising better policy to protect or enhance existing SOC stocks.

Distributions of arsenic and other heavy metals, and health risk assessments for groundwater in the Guanzhong Plain region of China.

The aim of this study was to evaluate the quality of shallow groundwater and deep groundwater in the Guanzhong Plain region of China, as well as the related health risk to humans. In total, 130 groundwater samples were collected comprising 116 from shallow groundwater (dug wells) and 14 from deep groundwater (drilled wells). The water samples were analyzed to determine the levels of As and 12 other heavy metals (Al, Cd, Mn, Cr, V, Fe, Ni, Cu, Zn, Co, Pb, and Mo). The results showed that the concentrations of As and other heavy metals in the deep groundwater samples were lower than the safe limits, but the Cr concentrations in some shallow groundwater samples exceeded the safe limits. The heavy metal pollution index and heavy metal evaluation index both showed that As and other heavy metals were pollutants at low levels in all of the shallow and deep groundwater sample. Health risk assessments showed that the deep groundwater samples had no associated non-carcinogenic health risks, whereas the shallow groundwater samples had non-carcinogenic health risks due to contamination with Cr and As. Some shallow groundwater samples had associated carcinogenic health risks due to contamination with Cr and As, whereas the deep groundwater samples only had carcinogenic health risks because of contamination with Cr. These results suggest that local residents and government departments should be made aware of Cr and As pollution in shallow groundwater.

Response of soil CO2 efflux to precipitation manipulation in a semiarid grassland.

Soil CO2 efflux (SCE) is an important component of ecosystem CO2 exchange and is largely temperature and moisture dependent, providing feedback between C cycling and the climate system. We used a precipitation manipulation experiment to examine the effects of precipitation treatment on SCE and its dependences on soil temperature and moisture in a semiarid grassland. Precipitation manipulation included ambient precipitation, decreased precipitation (-43%), or increased precipitation (+17%). The SCE was measured from July 2013 to December 2014, and CO2 emission during the experimental period was assessed. The response curves of SCE to soil temperature and moisture were analyzed to determine whether the dependence of SCE on soil temperature or moisture varied with precipitation manipulation. The SCE significantly varied seasonally but was not affected by precipitation treatments regardless of season. Increasing precipitation resulted in an upward shift of SCE-temperature response curves and rightward shift of SCE-moisture response curves, while decreasing precipitation resulted in opposite shifts of such response curves. These shifts in the SCE response curves suggested that increasing precipitation strengthened the dependence of SCE on temperature or moisture, and decreasing precipitation weakened such dependences. Such shifts affected the predictions in soil CO2 emissions for different precipitation treatments. When considering such shifts, decreasing or increasing precipitation resulted in 43 or 75% less change, respectively, in CO2 emission compared with changes in emissions predicted without considering such shifts. Furthermore, the effects of shifts in SCE response curves on CO2 emission prediction were greater during the growing than the non-growing season.

Rainfall partitioning characteristics and simulation of typical shelter forest in Chinese Mu Us Sandy Land.

Numerous shelter forests have been established to combat desertification in the Mu Us Sandy Land, China. Shelter forests modify the characteristics of the underlying surface and affect the regional water cycle by altering rainfall partitioning. Understanding the rainfall partitioning process and its controlling factors for indigenous and exotic species is crucial for vegetation restoration and sustainable soil water management. This study developed an event-based rainfall partitioning process for three typical shelter forests. Indigenous vegetation, Amygdalus pedunculata Pall. (A. pedunculata), and two exotic species, Amorpha fruticosa L. (A. fruticose) and Pinus sylvestris var. mongholica Litv. (P. sylvestris), were observed during the rainy seasons (July and August) of 2021 and 2022. The results showed that throughfall, stemflow, and interception loss constituted 71.01 %, 8.23 %, and 20.76 % of rainfall, respectively, for A. pedunculata. The corresponding values were 74.65 %, 8.47 %, and 16.88 % for A. fruticose and 73.27 %, 1.44 %, and 25.29 % for P. sylvestris. Compared with the introduced P. sylvestris, the shrub canopy showed a greater funneling ratio and was conducive to recharging soil water by precipitation. The amount and intensity of rainfall were significantly correlated with the rainfall partitioning characteristics, whereas the correlation between rainfall duration and partitioning was insignificant. Based on the results of the revised Gash model, the stemflow was primarily influenced by the percentage of rainfall diverted to the stemflow. The interception loss for P. sylvestris was primarily influenced by the canopy storage capacity. However, the canopy storage capacity and the ratio of mean evaporation rate to mean rainfall intensity had significant effects on the interception loss in A. pedunculata and A. fruticose. It is necessary to comprehensively consider the vegetation type (tree/shrub and indigenous/exotic species) and the corresponding rainfall partitioning characteristics of shelter forests for the scientific construction and management of shelter forests in the Mu Us Sandy Land.

Analysis of soil water use by exotic and native vegetation in a semi-arid area and their associated interspecific competition.

The exotic vegetation used in dryland vegetation restoration projects is characterized by its fast-growing and deep-rooted system, which enables it to expedite the restoration of ecosystem functions and enhance biodiversity. However, the interspecific relationship between exotic and native vegetation and soil water uptake in these restored ecosystems remains unclear, limiting our ability to evaluate the succession process and sustainability of restored ecosystems. In this study, stable isotope techniques and a proportional similarity index were used to investigate soil water use strategies and interspecific relationships between exotic and native vegetation. The results showed significant differences between the soil water use strategies of both exotic and native vegetation between seasons and species, where the proportions of deep soil water (30-100 cm) used by exotic shrubs (Caragana korshinskii) and exotic grass (Medicago sativa) were significantly higher than those used by the co-occurring native grass (Stipa bungeana) (p < 0.05). As soil water storage declined, exotic vegetation increased its utilization of deep soil water, whereas native grasses relied more on surface water (0-10 cm). This suggests that deep-rooted exotic vegetation has greater adaptability and access to water resources than shallow-rooted native vegetation. However, a prolonged decline in soil water storage led to increased competition for surface soil water (0-30 cm) between the exotic and native vegetation. This may increase the risk of degradation of exotic vegetation, particularly in situations with lower soil water content in the deep layers. Overall, this study highlights the variation in water-use strategies and interspecies relationships between exotic and native vegetation and their implications for ecosystem succession, which provides valuable insights for developing future vegetation restoration strategies and managing restored ecosystems.

Characteristics, sources and influencing factors of atmospheric deposition of microplastics in three different ecosystems of Beijing, China.

As the research on microplastics (MPs) has intensified, more attention has been paid to MPs deposition in the atmosphere. This study further explores and compares the characteristics, the possible sources and influencing factors of deposition of MPs in three different ecosystems: forest, agricultural and residential area in Beijing. It was found that the deposited plastics were mostly white or black fibres, with PET and RY as the main MPs types. The range of deposition fluxes was 67.06-461.02 item·m-2·d-1, with highest deposition in residential area and lowest in forest, significant differences in MPs characteristics between environments. Based on MPs composition and shape, combined with backward trajectory analysis, the main sources of MPs were found to be textiles. Deposition of MPs was found to be influenced by environmental and meteorological factors. Factors such as gross domestic product and population density had a significant impact on the deposition flux, while wind played a diluting role for atmospheric MPs. The study investigated the characteristics of MPs in different ecosystems which may help to understand the transport patterns of MPs and is of great importance for the management of MPs pollution.

Contrasting response of soil microbiomes to long-term fertilization in various highland cropping systems.

Soil microbiomes play important roles in supporting agricultural ecosystems. However, it is still not well-known how soil microbiomes and their functionality respond to fertilization in various cropping systems. Here we examined the effects of 36 years of phosphorus, nitrogen, and manure application on soil bacterial communities, functionality and crop productivity in three contrasting cropping systems (i.e., continuous leguminous alfalfa (AC), continuous winter wheat (WC), and grain-legume rotation of winter wheat + millet - pea - winter wheat (GLR)) in a highland region of China's Loess Plateau. We showed that long-term fertilization significantly affected soil bacterial communities and that the effects varied with cropping system. Compared with the unfertilized control, fertilization increased soil bacterial richness and diversity in the leguminous AC system, whereas it decreased those in the GLR system. Fertilization, particularly manure application, enlarged the differences in soil bacterial communities among cropping systems. Soil bacterial communities were mostly affected by the soil organic carbon and nitrogen contents in the WC and GLR systems, but by the soil available phosphorous content in the AC system. Crop productivity was closely associated with the abundance of fertilization-responsive taxa in the three cropping systems. Our study highlights that legume and non-legume cropping systems should be disentangled when assessing the responses of soil microbial communities to long-term fertilizer application.

Vertical distribution of soil available phosphorus and soil available potassium in the critical zone on the Loess Plateau, China.

Soil available phosphorus (SAP) and soil available potassium (SAK) are important elements in the growth of plants. However, limited data are available regarding the vertical distribution of SAP and SAK in deep soil profiles. In this study, we investigated the vertical variations in SAP and SAK in the critical zone on the Loess Plateau (50-200 m), China, by using classical statistical and geostatistical methods. The soil samples were collected from the top of the soil profile down to the bedrock by soil core drilling at five typical sites. SAP decreased throughout the profile. Whereas the SAK exhibited an increasing trend at all sites. The mean SAP concentration ranged from 0.94 to 32.56 mg kg-1 at the sampling sites and the SAK concentration ranged from 44.51 to 229.31 mg kg-1. At all of the sampling sites, SAK was significantly positively correlated with the depth and clay content, but there was a significantly negative correlation between the SAK and the sand content. The exponential model could fit most variograms of SAP and SAK at all sampling sites. The results obtained in this study to improve our comprehension of the SAP or SAK distribution conditions on the Loess Plateau, which is important for reasonable fertilizer application and vegetation planting practices.

Erosion reduces soil microbial diversity, network complexity and multifunctionality.

While soil erosion drives land degradation, the impact of erosion on soil microbial communities and multiple soil functions remains unclear. This hinders our ability to assess the true impact of erosion on soil ecosystem services and our ability to restore eroded environments. Here we examined the effect of erosion on microbial communities at two sites with contrasting soil texture and climates. Eroded plots had lower microbial network complexity, fewer microbial taxa, and fewer associations among microbial taxa, relative to non-eroded plots. Soil erosion also shifted microbial community composition, with decreased relative abundances of dominant phyla such as Proteobacteria, Bacteroidetes, and Gemmatimonadetes. In contrast, erosion led to an increase in the relative abundances of some bacterial families involved in N cycling, such as Acetobacteraceae and Beijerinckiaceae. Changes in microbiota characteristics were strongly related with erosion-induced changes in soil multifunctionality. Together, these results demonstrate that soil erosion has a significant negative impact on soil microbial diversity and functionality.

Impacts of shrub introduction on soil properties and implications for dryland revegetation.

The intensive introduction of shrubs to drylands can alter species composition and affect a series of biotic and abiotic processes. This topic has attracted increasing attention by researchers. To assess the response of soil properties to vegetation succession in arid regions of China, we measured the soil water content (SWC) to a depth of 5-m and determined soil properties of surface (0-5 cm) and subsurface (20-25 cm) layers in areas of natural grasses (NGs) and planted shrubs (PSs). The patch size of Caragana korshinskii shrubs resulted in different soil water storage losses (small shrub patch: 206.67 ± 35.58 mm; medium shrub patch: 416.88 ± 35.12 mm; large shrub patch: 588.63 ± 72.00 mm; degraded shrub patch: 740.54 ± 17.00 mm). Shrub cover showed an initial increase but then decreased as shrubs extracted soil water from the deep soil layers (>1 m). The species richness index in the PSs decreased with increasing shrub patch sizes. Surface soil organic carbon (SOC), extractable nitrogen (NH4+-N and NO3--N), and available phosphorous contents and saturated soil hydraulic conductivity (Ks) in the PSs were all significantly (p < 0.05) lower than those in NGs. Soil particles in the range of 0.002-0.2 mm explained 28.0% and 47.3% of the total variability of these surface indices under NGs and PSs, respectively. The differences in SOC, NH4+-N, NO3--N, Ks, and field capacity between the surface and subsurface layers declined significantly (p < 0.05). The introduction of shrubs affected the plant community by increasing the spatial heterogeneity of soil resources (e.g. water and nutrient contents). Therefore, the strong feedback between SWC and vegetation succession should be carefully considered when revegetating drylands. The evaluation of regional soil property responses to vegetation succession aids in a better understanding of soil water-vegetation feedback and provides important implications for future revegetation in arid regions.

Insight into the vertical characteristics of dissolved organic matter in 5-m soil profiles under different land-use types on the Loess Plateau.

Dissolved organic matter (DOM) is a natural chemical component of all soils and influences soil organic pollutant migration, nutrient cycling, and global climate change. Previous field studies have focused on a single ecosystem, such as cropland, grassland, or forestland. However, the potential effect of different land-use types on the vertical distribution of soil DOM quantity and quality remains unclear. This study investigated the vertical characteristics of DOM in 5-m soil profiles under different land-use types (cropland, grassland, and forestland) on the Loess Plateau. The data from ultraviolet-visible spectral and parallel factor analysis of fluorescence excitation-emission matrix spectrophotometry were combined. These results indicated that the mean content of dissolved organic carbon (DOC) in the 30-yr forestland (203.33 mg kg-1 soil) was the highest, and the lowest was observed in the cropland (83.70 mg kg-1 soil). Meanwhile, the mean DOC content of the forestland increased through time, particularly after 20 years. In other words, afforestation activities only significantly affected soil DOM after a long time (over 20 years). The DOC content of the cropland initially increased and then decreased with soil depth in the 1-m soil profiles, which may be related to agricultural activities. Three fluorescence components, including two humic acid-like substances (C1 and C3) and a tryptophan-like substance (C2), were identified from all samples. The humic acid-like components significantly decreased by 51% with soil depth, while the tryptophan-like component increased by 49%, particularly in the cropland. The variation in ultraviolet-visible spectral and optical indexes also indicated that soil DOM was dominated by both microbial and terrestrial sources. These findings help to understand the dynamics of DOC in deep soil profiles and the biogeochemical effects of DOM in the natural environment.

What is the mass of loess in the Loess Plateau of China?

The Loess Plateau of China (LP) has the largest and thickest loess deposits in the world. Quantifying the amount of loess in the LP is crucial for investigating the accumulation and erosion of loess, and determining the regional soil and water resource capacity. We used loess thickness data, a pedotransfer function for bulk density (BD), and the clay content data observed in 242 sites across the LP to derive the BD of loess and then estimate the loess mass and its distribution across the LP. The results indicated that the average BD of loess between the surface and bedrock is 1.58 g cm-3, varying from 1.18 to 1.87 g cm-3. The total loess mass is approximately 5.45 × 1013 t, and the average loess mass over an area of 1 m2 is 169 t, ranging from 1.36 to 585 t. The greatest mass of loess is in the south-central of the LP while the lowest mass of loess is in the northwest and river valley areas. Our estimate of loess mass provides key data for calculating water, carbon, and nutrient storages in the LP, which improves our understanding of soil-water processes and ecohydrological systems in this landscape.

Permanent dry soil layer a critical control on soil desiccation on China's Loess Plateau.

The wide spread of dry soil layers (DSL) in China's Loess Plateau region has negative effects on the ecosystem, including soil degradation and vegetation failure. To understand the temporal persistence of DSL, a ca. 860 km south-north transect was established and soil water content of the 0-5 m depth soil layer repeatedly measured for a period of four years. The results indicated that DSL varied with time and had a distribution area over 21.5-47.0% in the 860 km transect during the study period. The DSL could be divided into temporary and permanent types based on the length of period for which the soil remains dry. While temporary DSL is recoverable, permanent DSL (which existed in 47 out of 86 sites) was apparently unrecoverable as it persisted throughout the observation period. Permanent DSL was characterized by high temporal persistence, severe soil desiccation and thick dry layers; all of which suggested severe negative effect on the ecosystem. Non-climatic factors, rather than climate factors, contributed more to the formation of permanent DSL in the study area. Thus, it was suggested that policies and measures should be enacted to control especially permanent DSL formation in the region.

[The genetic effects of IGF2 gene intron3 variance in pigs].

A mispairing PCR-RFLP technique was applied in this study to determine the Insulin-like Growth Factor 2(IGF2) gene intron3 G3072A mutation in an outbred Landrace and Large White, and the gelded boars from Landrace x Large White cross. The difference of corresponding traits and the genetic effects of the boars inherited from parental A allele and inherited from parental G allele were analyzed. The results indicated that comparing with the boars inherited from parental G allele, the boars inherited from parental A allele increased significantly in the circumference 3.06% (P< 0.05) and index of body 3.01% (P< 0.05), respectively. The boars inherited from parental A allele had a significantly less average buttock fat thickness (15.31%, P< 0.01), thorax-waist fat thickness (23.74%, P< 0.01), skin thickness 9.38% (P< 0.01), fiber density (20.03%, P< 0.01) and had more less 6th-7th rib fat thickness (20.27%, P< 0.05), tendernce (17.32%, P< 0.05), and had more thick shoulder fat thickness (7.97%, P< 0.05), and had bigger the loin eye area (22.58%, P< 0.01) and fiber cross-sectional area (32.70%, P< 0.01) and fiber diameter (15.38%, P< 0.01) and lean meat (2.18%, P< 0.01) than the boars inherited from parental G allele. The results were suggested that the parental A allele has highly significant genetic effects in improving pig body development and carcass lean percent by increasing fiber diameter and the loin eye area, and decreasing the skin thickness and fat percent.

Deep soil water storage varies with vegetation type and rainfall amount in the Loess Plateau of China.

Soil-water storage in a deep soil layer (SWSD), defined as the layer where soil water is not sensitive to daily evapotranspiration and regular rainfall events, functions as a soil reservoir in China's Loess Plateau (LP). We investigated spatial variations and factors that influence the SWSD in the 100-500 cm layers across the entire plateau. SWSD generally decreased from southeast to northwest following precipitation gradient, with a mean value of 587 mm. The spatial variation in the SWSD in grassland was the highest, followed by protection forests, production forests and cropland. Variation in the >550 mm rainfall zone was much lower than that in the <550 mm zone. The significant influencing variables explained 22.3-65.2% of the spatial variation in SWSD. The joint effect of local and climatic variables accounted for most of the explained spatial variation of SWSD for each vegetation type and the <450 mm rainfall zone. Spatial variation of SWSD, however, was dominantly controlled by the local variables in the 450-550 and the >550 mm rainfall zones. Therefore, regional models of SWSD for a specific vegetation need to incorporate climatic, soil and topographic variables, while for a rainfall zone, land use should not be ignored.

Phases and rates of iron and magnetism changes during paddy soil development on calcareous marine sediment and acid Quaternary red-clay.

Dynamic changes in Fe oxides and magnetic properties during natural pedogenesis are well documented, but variations and controls of Fe and magnetism changes during anthropedogenesis of paddy soils strongly affected by human activities remain poorly understood. We investigated temporal changes in different Fe pools and magnetic parameters in soil profiles from two contrasting paddy soil chronosequences developed on calcareous marine sediment and acid Quaternary red clay in Southern China to understand the directions, phases and rates of Fe and magnetism evolution in Anthrosols. Results showed that paddy soil evolution under the influence of artificial submergence and drainage caused changes in soil moisture regimes and redox conditions with both time and depth that controlled Fe transport and redistribution, leading to increasing profile differentiation of Fe oxides, rapid decrease of magnetic parameters, and formation of diagnostic horizons and features, irrespective of the different parent materials. However, the initial parent material characteristics (pH, Fe content and composition, weathering degree and landscape positions) exerted a strong influence on the rates and trajectories of Fe oxides evolution as well as the phases and rates of magnetism changes. This influence diminished with time as prolonged rice cultivation drove paddy soil evolving to common pedogenic features.