Deep Soil Research Articles

Temporal and Spatial Distribution and Risk Assessment of Volatile Chlorinated Hydrocarbons in Soils of Typical Industrial Parks in Chongqing Under the “Dual Carbon” Background

ABSTRACT In the context of China’s “Dual Carbon” initiative, controlling volatile compounds (VOCs) in industrial park soils was crucial for pollution control and carbon mitigation efforts. This study examined the distribution and risks of chlorinated hydrocarbons in the soils of Chongqing’s chemical and mechanical industrial parks. Through site surveys, in situ sampling, pollutant extraction and detection, and soil microbial diversity sequencing, we identified a higher pollution risk in chemical parks (detection rate of 18.5%) and compared to mechanical parks (1%). Surface soils exhibited greater pollutant concentrations (11.8%) than deeper soils (8.8%), with higher contamination levels in winter (27.8%) than in summer (9.3%). Microbial diversity analysis revealed richer microbial communities in summer, suggesting their role in the natural degradation of pollutants, with Proteobacteria dominating but remaining largely functionally uncharacterized. Trichloroethylene and tetrachloroethylene were the primary detected pollutants, though at concentrations below regulatory thresholds. These findings provided crucial data for refining carbon emission policies and environmental management strategies in industrial parks under the “Dual Carbon” framework.

Rapid urbanization through cropland encroachment in the Jiangsu-Zhejiang-Shanghai region of China leads to substantial soil organic carbon loss

Abstract Soil organic carbon (SOC) is a major terrestrial carbon reservoir, crucial for the global carbon cycle and climate change. However, the impact of urbanization-induced cropland encroachment on SOC remains underexplored. This study quantified SOC loss in the top 20 cm (SOC20) and 100 cm (SOC100) soil layers in the Jiangsu-Zhejiang-Shanghai (JZH) region from 1985 to 2019 using high-resolution China Land Cover Dataset and multi-temporal SOC maps. Our results show that the cumulative cropland encroachment area in the study area reached 18,925.65 km2, approximately three times the area of Shanghai. The encroached areas of cropland in Jiangsu, Zhejiang, and Shanghai accounted for 59.72%, 31.49%, and 8.79% of the total, respectively. The cumulative SOC100 loss in the JZH region was approximately 65.31 ± 32.45 Tg C, with the SOC20 loss contributing about 32.97%, emphasizing the importance of deep SOC pool. The cumulative SOC20 (SOC100) losses in Jiangsu, Zhejiang, and Shanghai contributed approximately 55.36% (57.74%), 35.76% (31.96%), and 8.87% (10.3%) to the total SOC loss in the JZH region, respectively. Moreover, the annual average SOC100 loss accounted for about 8.6% to 25.59% of the terrestrial carbon sink flux (11.24 Tg C yr–1) in the JZH region, emphasizing that SOC loss due to cropland encroachment cannot be overlooked when evaluating the regional carbon sink capacity. Additionally, the positive correlation between SOC loss and regional Gross Domestic Product highlights the trade-off between economic development model of urban expansion through cropland encroachment and the resulting substantial SOC loss. This study emphasizes the importance of assessing the impacts of urbanization on regional SOC stocks, especially with regard to deep soil, and provides scientific insights for future urban planning and land management in this region.

Evaluating the Strength and Durability Properties of Geopolymer-Stabilized Soft Soil for Deep Mixing Applications

Soft soil poses serious challenges and is unsuitable for engineering projects because of its insufficient bearing capacity, low shear strength, and high compressibility. Deep soil mixing (DSM) is one of the most popular methods of enhancing soft soil qualities, such as increased bearing capacity and reduced settling, which are critical for building any structure. The environmental effects of creating binders such as cement and lime make it crucial to identify alternative materials for geotechnical applications. This study employed fly ash (class C) --based geopolymer to investigate its effectiveness as an environmentally friendly substitute for cement for DSM applications. The experimental program included unconfined compressive strength, flexure strength, and durability tests. The parameters in the study are binder content (10, 15, and 20%) and activator/binder ratio (0.4, 0.6). Results revealed that UCS and flexural strength, GP-treated soil were in the range of 0.9–5.3 and 0.8–1.5 MPa, respectively (depending on the ratio of fly ash and activator). These strengths were even higher than those of cement-stabilized soil. The geopolymer-treated specimens exhibited excellent endurance over the wetting-drying cycle, with a modest weight loss of less than 4.5%. A binder dosage of more than 10% and an AC ratio of 0.6 were recommended to meet DSM application guidelines. The current study concludes that employing a fly ash-geopolymer binder to stabilize soft soil is an effective alternative to cement in DSM applications.

Assessing the impact of multi-source environmental variables on soil organic carbon in different land use types of China using an interpretable high-precision machine learning method

To explore the impact of environmental factors on soil organic carbon (SOC) with machine learning (ML) model is of great significance for mitigating climate change and soil carbon sequestration and emission reduction. However, the traditional ML model is limited by the hyperparameter adjustment of artificially trial-and-error experimentation and the inexplicability of fitting process, and the precision and performance of ML model cannot be fully utilized. For the end, this study developed a tree-structured Parzen estimator-extreme gradient boosting (TPE-XGBoost) method based on SHapley additive explanations (SHAP) analysis to analyze the response of climate, human activities, soil properties and terrain for SOC (0-200cm) in different land use types of China. The results of descriptive statistics described the order of SOC content: forest land > grassland > cultivated land > unused land. With the increase of soil depth, the SOC content of all land types decreased continuously, and the values indicate a left-skewed non-normal distribution. The fitting accuracy (R2) of TPE-XGBoost model for SOC content was greater than 0.8. At the depth of 0-5cm, the prediction accuracy of cultivated land (R2 = 0.96), grassland (R2 = 0.93), forest land (R2 = 0.95) and unused land (R2 = 0.95) was the highest. The result of SHAP analysis showed that the factors that contributed the most to the fitting accuracy of cultivated land, grassland, forest land and unused land in all depths were temperature, soil pH, temperature and elevation. From surface to deep soil, the mean SHAP value showed a downward trend, indicating that the driving force of environmental factors on the content of SOC gradually weakened. The individual explanations of the variance partitioning (VP) analysis of climate, terrain, and soil property for cultivated land (0-200cm), forest land (30-60cm), and unused land (0-200cm) was as high as 0.32, 0.17, and 0.16, respectively, which indicated that these environmental factors had a high response to SOC content. It is found that the appropriate temperature not only promotes plant roots to obtain nutrients, but also interacts with soil pH on microorganisms, thereby increasing the SOC content. The results confirm that the TPE-XGBoost model based on SHAP analysis can reliably explain the nonlinear driving effect of environmental factors on the SOC, which provides credible decision support for accounting carbon budget and carbon sequestration in large-scale regions.

Effects of anecic Amynthas aspergillum on the proportion and depth of straw-derived carbon input into soil

Straw mulching significantly affects the soil organic carbon (OC) pool, but its positive effect on soil OC is limited by the slow decomposition rate and shallow depth. Increasing the conversion rate of straw-derived carbon (C) to soil OC and the depth affected are important for enhancing soil carbon storage and mitigating global climate change. Anecic earthworms feed on surface organic residues and dwell underground; and thus, they can carry surface straw directly underground. However, previous studies have focused on European earthworms, and it is still unclear how Chinese widely distributed earthworms, such as the anecic Amynthas aspergillum, affect the conversion rate of straw-derived C into soil OC and the depth affected, and whether these effects are related to soil properties. Using 13C tracing technology, we established treatments with and without A. aspergillum in soil with added straw to examine how A. aspergillum regulate the distribution of straw-derived OC in soil profiles during incubation for 31 days. Soil samples from the plow layer (PL) and plow pan layer (PP) of subtropical corn land were used in this study to represent two soils of different properties. Visible earthworm casts were not observed on the surface soil. A. aspergillum significantly increased the loss of surface straw by 86.1 % and 43.1 % in the PL and PP soils, respectively (p < 0.05). The conversion rate of straw-derived C into soil OC was 21.8 ± 0.5 % in the presence of earthworms in the PL soils, which was significantly greater than that without earthworms (7.9 ± 0.5 %, p < 0.05). The conversion rates were 8.0 % and 12.8 % in the absence and presence of earthworms, respectively, in the PP soils. The A. aspergillum increased the soil depth affected by straw-derived C input in the profiles of both the PL (to 10–20 cm) and PP soils (to 5–10 cm) compared with the treatments without earthworms (0–5 cm). Thus, anecic A. aspergillum promoted the decomposition of straw, enhanced the conversion of straw-derived C into soil OC and depth affected, and the effects of A. aspergillum were greater in the fertile soils. The underground casting behavior of A. aspergillum, may enhance the effects of incorporation of surface straw-derived C in deep soils. We suggest that earthworm regulation combined with straw return could be considered in sustainable agriculture.

Modelling of the trade-off between the deep soil moisture and vegetation restoration in the hilly area of the Loess Plateau, China

Excessive depletion of soil moisture by artificial forests in the vegetation restoration areas of the Loess Plateau has attracted widespread attention. To assess potential risks of soil moisture deficit, we needed on-site vegetation and soil sampling data, as well as UAV images from the Chaigou Watershed for three-dimensional analysis, combining both sampling and raster data. Three-dimensional surfaces for assessment of trade-off were established innovatively by the local regression and interpolation methods. The results indicated that soil moisture benefits at 20–40 cm depth are lower than at 0–20 cm due to infiltration and surface disturbance. In some areas of the Chaigou Watershed, grass and shrub-grass vegetation are facing risks of soil moisture deficit based on trade-off values (RSMD) and multiparameter evaluations. Analysis of deep soil water content variability revealed the moisture decreases significantly with the deepening of the soil layer in some plots. R (Richness), H (Shannon’s Diversity), Margalef, COHESION, and CONTAG were applicable in interpolation and fitted with the local regression model (R2 > 0.6) corresponding to the trade-off, but SPLIT was proven to be inapplicable in this study area. The zero trade-off inflection points were 6 %–8 %, while the trend inflection points were 7.5 %–9 % for soil moisture and vegetation indices of vegetation and landscape in typical sampling sites of the Chaigou Watershed. Three-dimensional fitting model is more comprehensive and effective in assessing deep soil moisture conditions and grass plots on shady slopes generally had the best trade-off status in this region.

Mycorrhizal Diversity on Roots of Silver Birch and Hybrid Aspen in Clonal Plantations in Northern Europe, Latvia

Mycorrhizal fungi contribute to crop growth, yields, and stress tolerance. In forests, common mycorrhizal networks are suggested to function as carbon storage and to transfer substances and signals between trees, thus likely contributing to their resilience. Such properties are crucial under increasing environmental stresses, particularly for clonal forestry. However, mycorrhizal communities in relation to tree field performances have been scarcely studied. In this study, mycorrhizal communities on the roots of clones of silver birch and hybrid aspen growing in distinct trials in deep automorphous mineral soils (podzolic and fluvic) under hemiboreal conditions were assessed using internal transcribed spacer sequencing, bioinformatics, and community analysis. The mycorrhizal communities were moderately rich/diverse and were mostly formed by generalist taxa (prevailingly ectomycorrhizal) common for the region. The differences in communities among the tree clones were estimated for silver birch, while for hybrid aspen, the productivity of clones was inversely related to the richness and diversity of the communities, suggesting a top-down effect of the host. Accordingly, some mycorrhizal taxa (e.g., Hyaloscypha sp.) showed clone-specific abundances indicating a preference for a specific host. These findings prompt further functional studies and highlight the need to consider genetic differences of forest regenerative material for maximizing mycorrhizal diversity, as well as for more effective inoculation.

Response of soil carbon and nitrogen stocks to irrigation - A global meta-analysis

Irrigation has profound influences on carbon (C) and nitrogen (N) stocks in agricultural soil. However, the global-scale irrigation effects on C and N pools in farmland soils, as well as the C: N ratio (C/N), remain unclear. This study integrates existing studies on C and N in irrigated farmland worldwide and investigates the responses of soil C and N concentrations, stocks, and the C/N to irrigation by meta-analysis. The results suggest that irrigation has a significantly positive impact on soil organic carbon (SOC) and total nitrogen (TN) stocks overall, with the stocks increase by 10.9 % and 7.4 %, respectively, and a 3.1 % increase in the C/N, but has no significant impact in soil microbial biomass carbon (MBC). The positive feedback of SOC (6.0 %) and TN (6.6 %) stocks in topsoil is more pronounced in response to irrigation than that in subsoil. The impact of irrigation on SOC stocks is greater in semi-arid regions and under flood irrigation. Furthermore, SOC stocks increase more in sandy and loamy soils compared to clay soil, while TN exhibits larger increases in clay soil. The results also indicate that the response of C/N to irrigation is more pronounced under the condition of deep soil, sandy soil, and semi-arid regions. The influence of irrigation on SOC stocks and the C/N increases with the duration of irrigation, while the impact on TN stocks tends to weaken. Our study deepens the understanding of the mechanisms behind irrigation's effects on soil C and N stocks and therefore provides theoretical insights for the management of soil fertility in irrigated agriculture.

Assessing the Effectiveness of Satellite and UAV-Based Remote Sensing for Delineating Alfalfa Management Zones Under Heterogeneous Rootzone Soil Salinity

Site-specific application of agricultural inputs is crucial for optimizing resource utilization in alfalfa (Medicago sativa L.) production and addressing challenges such as soil salinity. The main objective of this study was to assess the effectiveness of PlanetScope and UAV-based NDVI imagery for delineating alfalfa management zones under heterogeneous rootzone soil salinity. The research was conducted in the alfalfa field located in Imperial Valley, CA. The extent of rootzone soil salinity was assessed using Electromagnetic induction (EMI) technology and deep soil sampling. Reference management zones were then defined using the soil salinity (ECe) map derived from apparent electrical conductivity (ECa) data. Additionally, a time series of NDVI images from PlanetScope imagery and an NDVI image captured using an unmanned aerial vehicle were used to delineate remote sensing-based management zones. Laboratory analysis of disturbed soil samples collected at various depths provided soil physicochemical property data. Soil salinity of the samples ranged from 2.2 to 13.4 dS m−1 with a moderate level of variability (CV = 37.7%). ECe-based management zones accounted for approximately 83% of the field's variability and exhibited substantial differentiation among delineated zones concerning diverse soil properties, including ECa, ECe, gravimetric water content, Mg2+, boron, Ca2+, Na+, and Cl−. Notably, NDVI images effectively captured field variability on par with ECe-based zoning. Moreover, NDVI images recommended the same optimal number of zones (i.e., three) to address the field's variability, aligning with the ECe-based zoning approach. Our findings highlight that heterogeneity of soil salinity in the root zone primarily impacts the variability of alfalfa NDVI early in the growing season. Consequently, this early stage emerges as the most opportune timeframe for NDVI-based zoning for rapid assessment of rootzone soil salinity concerns.

Heavy metals in roadside soil along an expressway connecting two megacities in China: Accumulation characteristics, sources and influencing factors

Transportation is widely recognized as a significant contributor to heavy metal (HM) pollution in roadside soils. A better understanding of HM pollution in soils near expressways is crucial, particularly given the rapid expansion of expressway transportation in China in recent years. In this study, 329 roadside topsoil samples were collected along the Beijing-Tianjin Expressway, which connects two megacities in China. Chemical analysis showed that HM concentrations in the soil samples were generally below national limits. The mean pollution index (Pi) values for As, Cr, Cu, Ni, Pb, and Zn ranged from 0.94 to 1.01, while Cd and Hg exhibited slightly higher mean Pi values of 1.19 and 1.13, respectively. The Nemerow integrated pollution index values for all samples ranged from 0.71 to 4.97, with a mean of 1.26. This suggests a slight enrichment of HM above natural background levels, especially for Cd and Hg. Source apportionment using positive matrix factorization revealed that natural sources contributed the most to soil HMs (64.51 %), followed by agricultural sources (19.15 %), traffic sources (9.77 %), and industrial sources (6.57 %). The Shapley additive explanation analysis, based on the random forest model, identified soil organic carbon, deep soil HM content, altitude, total soil K2O, urbanization composite impact index, and total soil P as primary influencing factors. This indicates that the impact of transportation on roadside soils along the Beijing-Tianjin Expressway is currently relatively limited. The prominent influence of soil properties and altitude underscored the importance of “transport” and “receptor” in the soil HMs accumulation process at the local scale. These findings provide critical data and a scientific basis for decision-makers to develop policies for expressway design and roadside soil protection.

Distribution of vanadium in the pedosphere of China and its natural and anthropogenic influencing factors

Vanadium (V) is a strategic element in high demand in the industrial and pharmaceutical sectors. However, anthropogenic activities, including mineral exploration and industrial emissions, increase the risk of V contamination in soils. Consequently, research on V in the fields of mineral exploration and environmental pollution has garnered increasing attention. The China Geochemical Baseline (CGB) Project has conducted the first comprehensive collection and analysis of 12,201 rock samples, 3,382 top soil samples, and 3,380 deep soil samples in mainland China and the data was analysed in this study. High V concentrations occurred in soils in southern and northern China, and that V concentration were scattered in northern China. The concentration of V in soils was influenced by several natural factors, including tectonic activity, the distribution of intermediate–basic rocks (especially basalts) and black rock series; the distribution of laterites, and the occurrence of V deposits. Additionally, certain regions with high V concentrations were impacted by anthropogenic factors, primarily mining and smelting. This study, utilizing fundamental comparative data offered by the CGB Project, presents a comprehensive investigation of the spatial distribution characteristics of V, its migration, and enrichment mechanisms on a regional scale and also provides essential geochemical information on the detailed distribution of V in the pedosphere and rocks of mainland China.

The trade-off between soil water recovery and nitrate leaching following the orchard-to-cropland conversion in the Chinese Loess Plateau

A large-scale conversion of apple orchards into farmland has occurred in the tableland region of the Chinese Loess Plateau due to the aging of apple trees and the increase in pests and diseases. However, the impact of this conversion on soil desiccation recovery and soil nutrient transportation remains unclear, posing a new challenge for sustainable agricultural development in the region. The study employed the space-time substitution approach to select a long-standing orchard and croplands that has been growing maize for 1-, 3-, 5-, and 10-years post-orchard conversion as sampling sites, to investigate the effects of recovery durations of orchard-to-cropland conversion on deep soil water recharge and residual nitrate dynamics, as well as the key factors driving these changes. The results indicated that within 5 years, the conversion led to a rapid recharge of desiccated deep soil (6–9 m), followed by a stable and slow increase in subsequent years. The annual soil water recovery rate in the deep soil was as high as 5.90 mm m−1 a−1. While, the increased water input also caused rapid leaching and accumulation of nitrate in the deep soil, with its peak depth increasing significantly from 3.4 m to 7.0 m over time (R2 = 0.92). Soil water was identified as the key factor influencing nitrate leaching, with a correlation coefficient of 0.48 (P < 0.05). In conclusion, orchard-to-cropland conversion effectively replenished the deep soil water in the short term but also accelerated soil nitrate leaching. Therefore, while large-scale conversion of orchards to farmland is undertaken, it is crucial to acknowledge the trade-off relationship involving the recharge of deep soil water and the subsequent increase in deep nitrogen leaching. The findings of this study hold significant implication for the management of water and nutrient resources after the conversion of orchards to farmland, highlighting the necessity to mitigate nitrogen leaching while soil water is being restored.

Propagation Characteristics and Influencing Factors of Meteorological Drought to Soil Drought in the Upper Reaches of the Shiyang River Based on the Copula Function

Drought propagation is a complex process, and understanding the propagation mechanisms of meteorological drought to soil drought is crucial for early warning, disaster prevention, and mitigation. This study focuses on eight tributaries in the upper reaches of the Shiyang River. Based on the Standardized Precipitation Index (SPI) and the Standardized Soil Moisture Index (SSMI), the Drought Propagation Intensity Index (DIP) and Copula function were applied to quantify the intensity and time of drought propagation from meteorological to soil drought and explored the drought propagation patterns at different temporal and spatial scales in these tributaries. Results showed that, in the 0–10 cm soil layer, the propagation intensity of meteorological drought to soil drought was peer-to-peer, with a propagation time of one month. In the middle (10–40 cm) and deep (40–100 cm) soil layers, propagation characteristics differed between the eastern and western tributaries. The western tributaries experienced stronger drought propagation intensity and shorter propagation times (2–4 months), while the eastern tributaries exhibited peer-to-peer propagation intensity with longer times (4–10 months). The large areas of forests and grasslands in the upper reaches of the Shiyang River contributed to strong land–atmosphere interactions, leading to peer-to-peer drought propagation intensity in the 0–10 cm soil layer. The eastern tributaries had extensive cultivated land, where irrigation during meteorological drought enhanced soil moisture, resulting in peer-to-peer propagation intensity in the middle (10–40 cm) and deep (40–100 cm) soil layers. In contrast, the western tributaries, with larger forest areas and widespread permafrost, experienced high water consumption and limited recharge in the 10–40 cm and 40–100 cm soil layers, leading to strong drought propagation.

Life on the edge: Microbial diversity, resistome, and virulome in soils from the union glacier cold desert

The high-latitude regions of Antarctica remain among the most remote, extreme, and least explored areas on Earth. Still, microbial life has been reported in these environments, with limited information on their genetic properties and functional capabilities. Although diverse autochthonous multidrug-resistant bacteria were found in Antarctic Peninsula soils, posing whether these soils could act as a source of resistance determinants that could emerge among pathogens, we still lack information regarding the resistome of areas closer to the South Pole. Moreover, no previous studies have evaluated the pathogenic potential of microbes inhabiting Antarctic soils. In this work, we combined metagenomic and culture-dependent approaches to investigate the microbial diversity, resistome, virulome, and mobile genetic elements (MGEs) in soils from Union Glacier, a cold desert in West Antarctica. Despite the extreme conditions, several bacterial phyla were found, predominating Actinomycetota and Pseudomonadota, with limited archaeal and fungal taxa. Contrastive with Ecology Glacier soils from King George Island, the Union Glacier soil bacterial community is significantly less diverse, mainly attributed to scarce moisture. We recovered >80 species-level representative genomes (SRGs) of predominant bacteria and an ammonia-oxidating nitrogen- and carbon-fixing archaeon from a novel species of Nitrosocosmicus. Several resistance and virulence genes were found in Union Glacier soils, similar to those in other Antarctic cold desert areas but significantly distinct from those observed in maritime Antarctica and other non-cryosphere biomes. Furthermore, we characterized bacterial isolates resistant to up to 24 clinical antibiotics, mainly Pseudomonas, Arthrobacter, Plantibacter, and Flavobacterium. Moreover, some isolates produced putative virulence factors, including siderophores, pyocyanins, and exoenzymes with hemolytic, lecithinase, protease, and DNAse activity. This evidence uncovers a largely unexplored resistome and virulome hosted by deep Antarctica's soil microbial communities and the presence of bacteria with pathogenic potential, highlighting the relevance of One Health approaches for environmental surveillance in this continent.

Heating up the roof of the world: tracing the impacts of in-situ warming on carbon cycle in alpine grasslands on the tibetan plateau

Abstract Climate warming may induce substantial changes in ecosystem carbon cycle, particularly for those climate-sensitive regions, such as alpine grasslands on the Tibetan Plateau. By synthesizing findings from in-situ warming experiments, this review elucidates the mechanisms underlying the impacts of experimental warming on carbon cycle dynamics within these ecosystems. Generally, alterations in vegetation structure and prolonged growing season favor strategies for enhanced ecosystem carbon sequestration under warming conditions. Whilst warming modifies soil microbial communities and their carbon-related functions, its effects on soil carbon release fall behind the increased vegetation carbon uptake. Despite no significant accumulation of soil carbon stock has been detected upon warming, notable changes in its fractions indicate potential shifts in carbon stability. Future studies should prioritize deep soil carbon dynamics, the interactions of carbon, nitrogen, and phosphorus cycles under warming scenarios, and the underlying biological mechanisms behind these responses. Furthermore, the integration of long-term warming experiments with Earth system models is essential for reducing the uncertainties of model predictions regarding future carbon-climate feedback in these climate-sensitive ecosystems.

Deep soil mixing and mass stabilization technology as flexible foundation under culvert boxes of pump station

Deep soil mixing and mass stabilization technology as flexible foundation under culvert boxes of pump station

Nearshore test field of wet deep soil mixing in Sweden

Nearshore test field of wet deep soil mixing in Sweden

Seasonal dynamics of water-use strategies and response to precipitation in different habitats of Nitraria L.

Nitraria L. is a dominant shrub in arid areas and its survival is hampered by low and unpredictable precipitation and uncertain future water conditions. However, little is known about the shrub’s water requirements or its response to precipitation. We determined the water utilization strategies of Nitraria L. species in habitats with different soil textures using the isotopic composition of xylem water and those of potential water sources (groundwater and vadose zone soil water). We used the MixSIAR model to quantify the relative contribution of potential water sources to shrub water in different soil textures. Our results showed that (1) The dynamic characteristics of water use of Nitraria L. species differed in different soil textures. In gravel soils, water in all soil layers was recharged by precipitation, and the shrub water source was controlled by precipitation with significant seasonal changes. In sandy and clay soils, shallow soil water was recharged by precipitation infiltration, but deep soil water was recharged by capillary rise. Nonetheless, the shrub water sources exhibited considerable seasonal fluctuations. During wet seasons, the shrub’s primary water sources were in shallow and mid-soil depths. However, during the dry season, the shrubs relied on groundwater, with more than half of their water originating in deep soil layers. (2) Nitraria L. species generally responded significantly to precipitation events, and those that survived in three soil textures were able to rapidly switch water sources to varying degrees. In particular, in sandy and gravelly soils, the proportion of deep soil water (24.3 %) and groundwater (16.2 %) used by Nitraria L. plants decreased significantly after a large precipitation event (e.g., 18.8 and 11.9 mm), shifting to a predominantly transient use of shallow soil water (48.5 %). Nitraria L. could shift water-absorbing soil layers according to the availability of potential water sources in different soil textures. This flexibility allows them to access the most readily available water more rapidly. Such optimal ecological adaptation can ensure that the plants will have an advantage in future predicted water shortage conditions.

Soils of Steppe areas in the Cis-Tundra Open Woodland Subzone on the Right Bank of the Kolyma River in Its Lower Reaches

The small steppe plots (steppoids) occur at southern slopes among open larch forests of the Lower Kolyma area (northeast Siberia). Depending on a soil parent material they are divided into petrophytic (on a bedrock eluvo-diluvium) and thermophytic (on a silty loam of the Yedoma formation (Ice Complex)) steppoids. A xeromorphic deep thawing soils with diverse humus accumulative horizons, high roots content and considerable water stable powder-like structure develop under steppoids. Soils of steppoids are zooturbated, especially thermophytic ones. They differ from those of the surrounding taiga landscape in the following features: decreased actual and potential acidity; higher content of exchange bases, water-soluble salts, carbonates and organic nitrogen; smaller ratio between concentrations of oxalate- and dithionite-extractable iron. Dark mulle-like forms of humus on the surface of mineral grains are widely represented among the microaccumulations of organic matter in taiga-steppe soils. The cryoxerozem soil formation trait shows better in the event of petrophytic steppoids. Despite the similarity of the soils of thermophytic steppoids with steppe cryoarid ones, they differ in the absence of carbonate accumulative and criohumic horizons as well as the relatively high acidity. Flow-carbonaceous grey-humus lithozem and flow-carbonaceous grey-humus or duff dark-humus soils are distinguished within the petrophytic steppoids just as surface-turbated (zooturbated) grey-humus or duff dark-humus soils are distinguished within the thermophytic steppoids.

The Impact of Extreme Precipitation on Soil Moisture Transport in Apple Orchards of Varying Ages on the Loess Plateau

The long-term cultivation of apple trees with deep root systems can significantly deplete moisture from the deep soil layers, while extreme rainfall events can rapidly replenish this moisture. Therefore, it is of great academic significance to investigate the influence of extreme precipitation on soil water dynamics in apple orchards of varying ages. This study was conducted on agricultural land and apple orchards of 12 years, 15 years, 19 years and 22 years (12 y, 15 y, 19 y and 22 y) to examine the impact of extreme precipitation on soil moisture transport. Soil moisture content and hydrogen and oxygen isotope (2H, 18O and 3H) data were collected before (October 2020 and May 2021) and after the extreme precipitation event (May 2022). This comprehensive analysis focuses on two aspects: soil moisture distribution and soil water recharge. The following main conclusions were drawn: (1) Extreme precipitation significantly enhanced deep soil water recharge in apple orchards: the depths of soil water supply for apple orchards of 12 y, 15 y, 19 y and 22 y were recorded as 282 mm, 180 mm, 448 mm and 269 mm, respectively. Correspondingly, the recharge depths were measured at approximately 12, 10, 10 and 7 m, respectively. It was observed that the recharge depth decreased with increasing age of the orchard. (2) Extreme precipitation did not have a significant impact on the values of δ2H and δ18O of deep soil moisture due to a limited infiltration depth through the piston flow mechanism (the maximum infiltration depth being around 3 m). (3) In agricultural land as well as apple orchards of 12 y, 15 y and 22 y in 2020, the tritium peak occurred at soil depths of 7.2, 6.9, 6.7 and 5.7 mm, respectively; in 2022, the corresponding values increased to 7.9, 8.7, 6.7 and 5.9 mm, respectively. This indicates that planting apple trees hindered the transport of soil moisture. The peak concentration of tritium in both agricultural land and different-aged apple orchards decreased after experiencing extreme precipitation. The findings will provide a scientific basis for water resource management and efforts toward ecological restoration on the Loess Plateau.