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The complex relationships within desert ecosystems and their environmental conditions are reflected in patterns of plant water use. Thus, understanding the sources of water used by plants in these areas is crucial for effective resource management. In this study, we investigated the water use pattern of Haloxylon ammodendron in Semnan province, in the central plateau of Iran, using the stable isotope analysis. We employed a simple, homemade cryogenic vacuum distillation (CVD) system to directly extract water from soil samples and different plant components for subsequent analysis by mass spectrometer. The contribution of each possible water source to the plant xylem water was estimated using the IsoSource mixing model. The pattern of δ 18O values in the xylem water of H. ammodendron indicated its reliance on groundwater as a primary water resource during the wet season. Additionally, the correlation of sand particles with both δ2H and δ18O was found to be 0.32. Moreover, the δ 18O values of H. ammodendron xylem water were mainly similar to those of groundwater, suggesting the species' dominant use of groundwater. The findings of this study provide valuable insights for strategically planting H. ammodendron to mitigate impacts on groundwater resources and ensure long-term sustainability in arid and semi-arid regions.

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Nutrient addition, particularly nitrogen, often increases plant aboveground biomass but causes species loss. Asymmetric competition for light is frequently assumed to explain the biomass-driven species loss. However, it remains unclear whether other factors such as water can also play a role. Increased aboveground leaf area following nitrogen addition and warming may increase transpiration and cause water limitation, leading to a decline in diversity. To test this, we conducted field measurements in a grassland community exposed to nitrogen and water addition, and warming. We found that warming and/or nitrogen addition significantly increased aboveground biomass but reduced species richness. Water addition prevented species loss in either nitrogen-enriched or warmed treatments, while it partially mitigated species loss in the treatment exposed to increases in both temperature and nitrogen. These findings thus strongly suggest that water limitation can be an important driver of species loss as biomass increases after nitrogen addition and warming when soil moisture is limiting. This result is further supported by a meta-analysis of published studies across grasslands worldwide. Our study indicates that loss of grassland species richness in the future may be greatest under a scenario of increasing temperature and nitrogen deposition, but decreasing precipitation.

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Expansive soils exhibit a relatively low permeability coefficient when structurally intact, allowing for their treatment as a homogeneous medium in calculations. However, the susceptibility of the slope's shallow area to numerous primary and secondary cracks under the influence of wetting and drying cycles challenges this approach. Failing to account for the impact of these surface cracks on the soil's permeability can result in a significant discrepancy between calculated and actual conditions. This study initially validated a predictive model for the soil-water characteristic curve that incorporates the effects of wetting and drying cycles. Subsequently, leveraging the fracture volume ratio parameter (pv) and the bimodal distribution characteristics of the dual-pore structure, we proposed a permeability coefficient model for expansive soils that considers fracture effects. This model was integrated with the validated soil-water characteristic curve model to facilitate the analysis of expansive soil's infiltration characteristics under cyclic wetting and drying conditions. The findings indicate that the predictive model accurately captures the hysteresis effect of expansive soil's soil-water characteristics. Moreover, the permeability coefficient model, which accounts for fractures, effectively reflects the infiltration properties of cracked expansive soil and enables the prediction and calculation of its permeability under multiple cycles of wetting and drying. This study introduces a predictive model for the soil-water characteristic curve, leveraging the hysteresis properties of expansive soil. Additionally, it presents a model for calculating the permeability coefficient of expansive soil, utilizing a dual-peak characteristic function. The development of these models establishes a theoretical basis for the computation and analysis of the soil's permeability attributes.

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This review assesses the feasibility of reusing treated wastewater for irrigation in agricultural soils as a strategy for nutrients recycling and mitigation of CO2 emissions. Through a literature review, it was examined wastewater sources enriched with carbon and nutrients, including municipal wastewater and associated sludge, vinasse, swine wastewater, as well as wastewater from the food industry and paper and pulp production. The review also explores the dynamics of organic matter within the soil, discussing the aspects related to its potential conversion to CO2 or long-term storage. It was found that industrial wastewaters, owing to their higher organic matter and recalcitrance, exhibit greater potential for carbon storage. However, the presence of pollutants in wastewater necessitates careful consideration, particularly concerning their impact on soil quality. Toxic metals, microplastics, and organic compounds emerged as significant contaminants that could accumulate in the soil, posing risks to ecosystem health. To mitigate the environmental impacts, it was evaluated various wastewater treatment technologies and their associated carbon emissions. While advanced treatments may effectively reduce the contaminant load and mitigate soil impacts, their adoption is often associated with an increase in CO2 emissions. Membrane bioreactors, microfiltration, ultrafiltration, and up-flow anaerobic sludge blanket reactors were identified as promising technologies with lower carbon footprints. Looking ahead, future research should aim to enhance the understanding of carbon dynamics in soil and validate the environmental impacts of treated wastewater disposal. Despite remaining uncertainties, the literature indicates a positive outlook for wastewater recycling in soil, offering a viable strategy for carbon storage and mitigation of greenhouse gas emissions.

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Freeze-thaw (FT) events profoundly perturb the biochemical processes of soil and water in mid- and high-latitude regions, especially the riparian zones that are often recognized as the hotspots of soil-water interactions and thus one of the most sensitive ecosystems to future climate change. However, it remains largely unknown how the heterogeneously composed and progressively discharged meltwater affect the biochemical cycling of the neighbor soil. In this study, stream water from a valley in the Chinese Loess Plateau was frozen at -10°C for 12 hours, and the meltwater (at +10°C) progressively discharged at three stages (T1 ∼ T3) was respectively added to rewet the soil collected from the same stream bed (Soil+T1 ∼ Soil+T3). Our results show that: (1) Approximately 65% of the total dissolved organic carbon and 53% of the total NO3--N were preferentially discharged at the first stage T1, with enrichment ratios of 1.60 ∼ 1.94. (2) The dissolved organic matter discharged at T1 was noticeably more biodegradable with significantly lower SUVA254 but higher HIX, and also predominated with humic-like, dissolved microbial metabolite-like, and fulvic acid-like components. (3) After added to the soil, the meltwater discharged at T1 (e.g., Soil+T1) significantly accelerated the mineralization of soil organic carbon with 2.4 ∼ 8.07-folded k factor after fitted into the first-order kinetics equation, triggering 125 ∼ 152% more total CO2 emissions. Adding T1 also promoted significantly more accumulation of soil microbial biomass carbon after 15 days of incubation, especially on the FT soil. Overall, the preferential discharge of the nutrient-enriched meltwater with more biodegradable DOM components at the initial melting stage significantly promoted the microbial growth and respiratory activities in the recipient soil, and triggered sizable CO2 emission pulses. This reveals a common but long-ignored phenomenon in cold riparian zones, where progressive freeze-thaw can partition and thus shift the DOM compositions in stream water over melting time, and in turn profoundly perturb the biochemical cycles of the neighbor soil body.

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In root research, hydroponic plant cultivation is commonly used and soil experiments are rare. We investigated the response of 12-day-old barley roots, cultivated in soil-filled rhizotrons, to different soil water potentials (SWP) comparing a modern cultivar (cv. Scarlett) with a wild accession ICB181243 from Pakistan. Water potentials were quantified in soils with different relative water contents. Root anatomy was studied using histochemistry and microscopy. Suberin and lignin amounts were quantified by analytical chemistry. Transcriptomic changes were observed by RNA-sequencing. Compared with control with decreasing SWP, total root length decreased, the onset of endodermal suberization occurred much closer towards the root tips, amounts of suberin and lignin increased, and corresponding biosynthesis genes were upregulated in response to decreasing SWP. We conclude that decreasing water potentials enhanced root suberization and lignification, like osmotic stress experiments in hydroponic cultivation. However, in soil endodermal cell suberization was initiated very close towards the root tip, and root length as well as suberin amounts were about twofold higher compared with hydroponic cultivation.

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Background: Soil water content is one of the critical indicators in agricultural systems. Visible/near-infrared hyperspectral remote sensing is an effective method for soil water estimation. However, noise removal from massive spectral datasets and effective feature extraction are challenges for achieving accurate soil water estimation using this technology. Methods: This study proposes a method for hyperspectral remote sensing soil water content estimation based on a combination of continuous wavelet transform (CWT) and competitive adaptive reweighted sampling (CARS). Hyperspectral data were collected from soil samples with different water contents prepared in the laboratory. CWT, with two wavelet basis functions (mexh and gaus2), was used to pre-process the hyperspectral reflectance to eliminate noise interference. The correlation analysis was conducted between soil water content and wavelet coefficients at ten scales. The feature variables were extracted from these wavelet coefficients using the CARS method and used as input variables to build linear and non-linear models, specifically partial least squares (PLSR) and extreme learning machine (ELM), to estimate soil water content. Results: The results showed that the correlation between wavelet coefficients and soil water content decreased as the decomposition scale increased. The corresponding bands of the extracted wavelet coefficients were mainly distributed in the near-infrared region. The non-linear model (ELM) was superior to the linear method (PLSR). ELM demonstrated satisfactory accuracy based on the feature wavelet coefficients of CWT with the mexh wavelet basis function at a decomposition scale of 1 (CWT(mexh_1)), with R2, RMSE, and RPD values of 0.946, 1.408%, and 3.759 in the validation dataset, respectively. Overall, the CWT(mexh_1)-CARS-ELM systematic modeling method was feasible and reliable for estimating the water content of sandy clay loam.

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Biochar (BC) is widely utilized as a soil amendment; however, for widely distributed seasonally frozen soils, the effect of BC on soil and the optimal utilization of BC during the freeze‒thaw process are still unclear. In this study, the effects of freeze‒thaw aged biochar (FT-BC) and BC on soil properties and wheat cultivation were systematically investigated, and the underlying interaction mechanism between BC and soil was explored. The results show that FT-BC dramatically reduces the adverse effects of freeze‒thaw cycles on soil, enhances wheat growth, and increases dry matter yield by 17.5 %, which is mainly attributed to the ability of FT-BC to maintain soil structure, reduce water loss rates to below 0.20 g/h, and decrease nitrogen leaching by more than 20 % during freeze‒thaw cycles. Additionally, fresh BC had a greater effect on the fixation of cadmium than FT-BC in the soil, reducing its accumulation in wheat by 22.5 %. Multiple characterizations revealed that the freeze‒thaw process increased the porosity and specific surface area of FT-BC, providing more sites for water and nitrogen adsorption, whereas the dissolved organic matter released from fresh BC had a better ability to trap cadmium. These findings provide insights into the interactions between BC and soil components during the freeze‒thaw process and suggest the optimized utilization of fresh BC and FT-BC for different soil repair purposes.

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Vermicompost is an organic material that is abundant in humic acids and nutrients. It is obtained through the bio-oxidation and stabilization processes carried out by earthworms. It has been proven to bring several benefits to different soil properties, including bulk density, soil structure, and plant available water capacity (PAWC). This investigation was conducted to fill the knowledge gap in some critical factors related to vermicompost application, specifically the short-term influence of a single vermicompost application with increasing doses on soil wettability and physical quality of differently textured soils. Water repellency of vermicompost and soil/vermicompost mixtures was investigated at different moisture contents by the water drop penetration time test, whereas physical quality was assessed by 35 soil indicators related to bulk density, soil water retention curve, and pore size distribution function. Despite vermicompost showed from strong to severe hydrophobicity at moisture content lower than the field capacity, amended soils were at the most slightly water repellent thus indicating that, under field conditions, the hydrophobicity attributable to soil amendment with vermicompost could be considered negligible. Soil physical quality was effectively affected by vermicompost addiction with different outcomes depending on soil texture. Indicators linked to PAWC generally increased at increasing the vermicompost rate in the coarse soils whereas no significant effect was observed for intermediate and fine soils. For example, plant available water capacity of coarse-textured soils increased from an average initial value of 0.056 cm3 cm-3 to an optimal value of 0.15 cm3 cm-3 when a vermicompost addition dose of about one-third by volume (34 %) was applied. In the finest soil, drainable porosity significantly increased from an initial value of 0.09 cm3 cm-3 to 0.23 cm3 cm-3 when the maximum vermicompost dose (43 %) was applied thus indicating that amendment could be effective in enhancing water and air circulation.

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The soil-water interactions of unsaturated diesel-contaminated soil are crucial for assessing pollution transport during thermal remediation. This paper aims to improve our understanding of this issue by measuring the matric suction of unsaturated contaminated kaolin and carrying out molecular dynamics simulations under thermal conditions. Results show that the increase in pollutant concentration could reduce the water retention capacity of diesel-contaminated kaolin due to changes in electrochemical properties and pore characteristics of samples, as well as a decrease in interfacial tension. On the other hand, pollutants formed a protective film on the kaolinite surface to act as a liquid bridge and prevent water loss at higher temperatures, as confirmed by Fourier transform infrared spectroscopy. With rising temperatures (50-60 °C), kaolin matric suction generally decreased with higher pollutant concentrations, but this trend was not very evident at lower pollution concentrations (0-10,000 mg/kg). In addition, molecular dynamics simulations were used to demonstrate the validity of these findings. The presence of pollutants might strengthen the interaction energy between kaolinite and water (for example, increasing from 276.52 kcal/mol (25 °C) and 267.95 kcal/mol (40 °C) at 8000 mg/kg to 296.54 kcal/mol (25 °C) and 292.46 kcal/mol (40 °C) at 10,000 mg/kg), thereby enhancing the water retention capacity of kaolin. In short, the study revealed that the coating of pollutants on kaolinite could act as a protective film, which binds water molecules through van der Waals and electric field forces and thereby reduces the sensitivity of water retention capacity to temperature.

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Root zone soil moisture (RZSM) is crucial for agricultural water management and land surface processes. The 1 km soil water index (SWI) dataset from Copernicus Global Land services, with eight fixed characteristic time lengths (T), requires root zone depth optimization (Topt) and is limited in use due to its low spatial resolution. To estimate RZSM at 100-m resolution, we integrate the depth specificity of SWI and employed random forest (RF) downscaling. Topographic synthetic aperture radar (SAR) and optical datasets were utilized to develop three RF models (RF1: SAR, RF2: optical, RF3: SAR + optical). At the DEMMIN experimental site in northeastern Germany, Topt (in days) varies from 20 to 60 for depths of 10 to 30 cm, increasing to 100 for 40-60 cm. RF3 outperformed other models with 1 km test data. Following residual correction, all high-resolution predictions exhibited strong spatial accuracy (R ≥ 0.94). Both products (1 km and 100 m) agreed well with observed RZSM during summer but overestimated in winter. Mean R between observed RZSM and 1 km (100 m; RF1, RF2, and RF3) SWI ranges from 0.74 (0.67, 0.76, and 0.68) to 0.90 (0.88, 0.81, and 0.82), with the lowest and highest R achieved at 10 cm and 30 cm depths, respectively. The average RMSE using 1 km (100 m; RF1, RF2, and RF3) SWI increased from 2.20 Vol.% (2.28, 2.28, and 2.35) at 30 cm to 3.40 Vol.% (3.50, 3.70, and 3.60) at 60 cm. These negligible accuracy differences underpin the potential of the proposed method to estimate RZSM for precise local applications, e.g., irrigation management.

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The development of water-saving management relies on understanding the physiological response of crops to soil drought. The coordinated regulation of hydraulics and stomatal conductance in plant water relations has steadily received attention. However, research focusing on grain crops, such as winter wheat, remains limited. In this study, three soil water supply treatments, including high (H), moderate (M), and low (L) soil water contents, were conducted with potted winter wheat. Leaf water potential (Ψleaf), leaf hydraulic conductance (Kleaf), and stomatal conductance (gs), as well as leaf biochemical parameters and stomatal traits were measured. Results showed that, compared to H, predawn leaf water potential (ΨPD) significantly reduced by 48.10% and 47.91%, midday leaf water potential (ΨMD) reduced by 40.71% and 43.20%, Kleaf reduced by 64.80% and 65.61%, and gs reduced by 21.20% and 43.41%, respectively, under M and L conditions. Although gs showed a significant difference between M and L, Ψleaf and Kleaf did not show significant differences between these treatments. The maximum carboxylation rate (Vcmax) and maximum electron transfer rate (Jmax) under L significantly decreased by 23.11% and 28.10%, stomatal density (SD) and stomatal pore area index (SPI) under L on the abaxial side increased by 59.80% and 52.30%, respectively, compared to H. The leaf water potential at 50% hydraulic conduction loss (P50) under L was not significantly reduced. The gs was positively correlated with ΨMD and Kleaf, but it was negatively correlated with abscisic acid (ABA) and SD. A threshold relationship between gs and Kleaf was observed, with rapid and linear reduction in gs occurring only when Kleaf fell below 8.70 mmol m-2 s-1 MPa-1. Our findings demonstrate that wheat leaves adapt stomatal regulation strategies from anisohydric to isohydric in response to reduced soil water content. These results enrich the theory of trade-offs between the carbon assimilation and hydraulic safety in crops and also provide a theoretical basis for water management practices based on stomatal regulation strategies under varying soil water conditions.

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Increases in hydrological extremes, including drought, are expected for Amazon forests. A fundamental challenge for predicting forest responses lies in identifying ecological strategies which underlie such responses. Characterization of species-specific hydraulic strategies for regulating water-use, thought to be arrayed along an 'isohydric-anisohydric' spectrum, is a widely used approach. However, recent studies have questioned the usefulness of this classification scheme, because its metrics are strongly influenced by environments, and hence can lead to divergent classifications even within the same species. Here, we propose an alternative approach positing that individual hydraulic regulation strategies emerge from the interaction of environments with traits. Specifically, we hypothesize that the vertical forest profile represents a key gradient in drought-related environments (atmospheric vapor pressure deficit, soil water availability) that drives divergent tree water-use strategies for coordinated regulation of stomatal conductance (gs) and leaf water potentials (ΨL) with tree rooting depth, a proxy for water availability. Testing this hypothesis in a seasonal eastern Amazon forest in Brazil, we found that hydraulic strategies indeed depend on height-associated environments. Upper canopy trees, experiencing high vapor pressure deficit (VPD), but stable soil water access through deep rooting, exhibited isohydric strategies, defined by little seasonal change in the diurnal pattern of gs and steady seasonal minimum ΨL. In contrast, understory trees, exposed to less variable VPD but highly variable soil water availability, exhibited anisohydric strategies, with fluctuations in diurnal gs that increased in the dry season along with increasing variation in ΨL. Our finding that canopy height structures the coordination between drought-related environmental stressors and hydraulic traits provides a basis for preserving the applicability of the isohydric-to-anisohydric spectrum, which we show here may consistently emerge from environmental context. Our work highlights the importance of understanding how environmental heterogeneity structures forest responses to climate change, providing a mechanistic basis for improving models of tropical ecosystems.

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Improving the water retention property of shallow soil in the inner dump is the key step in the sustainable development of mines. In recent years, the use of fly ash to improve the structure of the inner dump and polyacrylamide as an additive to enhance water retention was an effective method. The article used a physical model test, filter paper method, and microstructure analysis method to compare and analyze the water retention property and microstructure of slope-improved soil with different fly ash and polyacrylamide content. The results show that the combined use of fly ash and polyacrylamide improved the water retention property of the amended soil. Fly ash and polyacrylamide had a greater effect on the low suction stage of the amended soil. Polyacrylamide reacted with water and bound soil particles to form aggregates, and the structural unit bodies were a block structure. Fly ash was non-sticky and was a matrix of fine particles, which weakened the bonding effect of polyacrylamide, and reduced the aggregates of soil particles, and the structural unit bodies were a flocculated structure of aggregates mixed with matrix. This, in turn, enhanced the capillary action and improved the water retention performance of the improved soil. In addition, polyacrylamide could connect water molecules, further enhancing the water retention property of the improved soil. The combined use of fly ash and polyacrylamide improved the available water content of improved soil, providing a viable and sustainable solution for improving the comprehensive utilization of fly ash, and laid the foundation for land reclamation at the inner dump.

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Groundwater resources serve as the primary source of water in the agro-pastoral ecotone of northern China, where scarcity of water resources constrains the development of agriculture and animal husbandry. As a typical rainfed agricultural area, the agro-pastoral ecotone in Inner Mongolia is entirely dependent on groundwater for agricultural irrigation. Due to the substantial groundwater consumption of irrigated farmland, groundwater levels have been progressively declining. To obtain a sustainable irrigation pattern that significantly conserves water, this study faces the challenge of unclear water transport relationships among water, soil, and crops, undefined water cycle mechanism in typical irrigation units, and water use efficiency, which was not assessed. Therefore, this paper, based on in situ experimental observations and daily meteorological data in 2022-2023, utilized the DSSAT model to explore the growth processes of potato, oat, alfalfa, and sunflower, the soil water dynamics, the water balance, and water use efficiency, analyzed over a typical irrigation area. The results indicated that the simulation accuracy of the DSSAT model was ARE < 10%, nRMSE/% < 10%, and R2 ≥ 0.85. The consumption of the soil moisture during the rapid growth stage for the potatoes, oats, alfalfa, and sunflower was 7-13% more than that during the other periods, and the yield was 67,170, 3345, 6529, and 4020 kg/ha, respectively. The soil evaporation of oat, potato, alfalfa, and sunflower accounted for 18-22%, 78-82%; 57-68%, and 32-43%, and transpiration accounted for 40-44%, 56-60%, 45-47%, and 53-55% of ETa (333.8 mm-369.2 mm, 375.2 mm-414.2 mm, 415.7 mm-453.7 mm, and 355.0 mm-385.6 mm), respectively. It was advised that irrigation water could be appropriately reduced to decrease ineffective water consumption. The water use efficiency and irrigation water use efficiency for potatoes was at the maximum amount, ranging from 16.22 to 16.62 kg/m3 and 8.61 to 10.81 kg/m3, respectively, followed by alfalfa, sunflowers, and oats. For the perspective of water productivity, it was recommended that potatoes could be extensively cultivated, alfalfa planted appropriately, and oats and sunflowers planted less. The findings of this study provided a theoretical basis for efficient water resource use in the agro-pastoral ecotone of Northern China.

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Processes of water retention and movement and the hydraulic conductivity are altered in the rhizosphere. The aim of this study was to investigate the physical-hydric properties of soil aggregates in the rhizosphere of annual ryegrass (Lolium multiflorum) cropped in a Kandiudalfic Eutrudox, taking into account aspects related to soil aggregate stability. Soil aggregates from rhizosphere soil (RZS) and soil between plant rows (SBP) were used to determine soil water retention curves (SWRCs) and saturated hydraulic conductivity (Ksat). In addition, properties related to soil aggregate stability, such as water-dispersible clay, soil organic carbon (SOC), and microbial activity, were also assessed. The higher microbial activity observed in the RZS was facilitated by increased SOC and microbial activity, resulting in improved soil aggregation (less water-dispersible clay). For nearly all measured matric potentials, RZS had a higher water content than SBP. This was attributed to the stability of aggregates, increase in SOC content, and the root exudates, which improved soil water retention. The increase in total porosity in RZS was associated with improved soil aggregation, which prevents deterioration of the soil pore space and results in higher Ksat and hydraulic conductivity as a function of the effective relative saturation in RZS compared to SBP.

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The abundance of biodegradable microplastics (BMPs) is increasing in soil due to the widespread use of biodegradable plastics. However, the influence of BMPs on soil metal biogeochemistry, especially arsenic (As), under different water regimes is still unclear. In this study, we investigated the effects of two types of BMPs (PLA-MPs and PBAT-MPs) on As fractionation in two types of soils (black soil and fluvo-aquic soil) under three water regimes including drying (Dry), flooding (FL), and alternate wetting and drying (AWD). The results show that BMPs had limited indirect effects on As fractionation by altering soil properties, but had direct effects by adsorbing and releasing As during their degradation. Enzyme degradation experiments show that the degradation of PLA-MPs led to an increased desorption of 4.76 % for As(III) and 15.74 % for As(V). Synchrotron-based X-ray fluorescence (µ-XRF) combined with micro-X-ray absorption near edge structure (µ-XANES) analysis show that under Dry and AWD conditions, As on the BMPs primarily bind with Fe hydrated oxides in the form of As(V). Conversely, 71.57 % of As on PBAT-MP under FL conditions is in the form of As(III) and is primarily directly adsorbed onto its surface. This study highlights the role of BMPs in soil metal biogeochemistry.

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Mediterranean ecosystems are predicted to undergo longer and more intense summer droughts. The mechanisms underlying the response of herbaceous communities to such drier environments should be investigated to identify the resilience thresholds of Mediterranean rangelands. A 5-year experiment was conducted in deep and shallow soil rangelands of southern France. A rainout shelter for 75 days in summer imposed drier and warmer conditions. Total soil water content was measured monthly to model available daily soil water. Aboveground net primary production (ANPP), forage quality, and the proportion of graminoids in ANPP were measured in spring and autumn. Plant senescence and plant cover were assessed in summer and spring, respectively. The experimental years were among the driest ever recorded at the site. Therefore, manipulated summer droughts were drier than long-term ambient conditions. Interactions between treatment, community type, and experimental year were found for most variables. In shallow soil communities, spring plant cover decreased markedly with time. This legacy effect, driven by summer plant mortality and the loss of perennial graminoids, led to an abrupt loss of resilience when the extreme water stress index exceeded 37 mm 10 day-1, characterized by a reduction of spring plant cover below 50% and a decreased ANPP in rainy years. Conversely, the ANPP of deep soil communities remained unaffected by increased summer drought, although the presence of graminoids increased and forage nutritive value decreased. This study highlights the role of the soil water reserve of Mediterranean plant communities in modulating ecosystem responses to chronically intensified summer drought. Communities on deep soils were resilient, but communities on shallow soils showed a progressive, rapid, and intense degradation associated with a loss of resilience capacity. Notably, indexes of extreme stress were a better indicator of tipping points than indexes of integrated annual stress. Considering the role of soil water availability in other herbaceous ecosystems should improve the ability to predict the resilience of plant communities under climate change.

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The increasing atmospheric CO2 concentration is a global concern that affects the plant-bacteria-soil system. Previous studies have investigated plant growth and bacteria activity under CO2 enrichment. However, the effects of coupled elevated CO2 and biochar amendment on the interactions of soil and medicinal plants are not well understood. This study aims to investigate the medicinal plant-soil hydraulic interactions and rhizosphere bacteria communities under coupled CO2 enrichment and biochar conditions. Two levels of CO2 concentration (400, 1000 ppm) and two biochar dosages (3%, 5% by mass) were considered. Pseudostellaria heterophylla was used as the tested medicinal plant. During plant growth, coupled CO2 enrichment and biochar at 3% and 5% dosage increased the volumetric water content at a matric suction of 33 kPa by 97% and 82% respectively, which indicates enhanced water retention. The transpiration rate of P. heterophylla was slightly reduced by 11-30% with an increase in biochar dosage due to higher total suction, while it was significantly reduced by up to 57% due to CO2 enrichment. In the rhizosphere of P. heterophylla, elevated CO2 (1000 ppm) coupled with 3% biochar dramatically increase the relative abundance of Thaumarchaeota, which played an important role in C and N cycles. Moreover, coupled CO2 enrichment and biochar addition resulted in the highest bacterial richness, while 3% biochar at ambient CO2 induced the highest bacterial diversity. This study provides a basis for understanding the medicinal plant-bacteria-soil system under CO2 enrichment and biochar conditions.

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Biochar exhibits numerous advantages in enhancing the soil environment despite a few limitations due to its lower surface energy. Nanomodified biochar combines the advantages of biochar and nanoscale materials. However, its effects on water infiltration and N leaching in a clayey soil remain unclear. Therefore, this study prepared rice straw nano-biochar by a ball milling method, and investigated its physicochemical properties and effects of bulk biochar and nano-biochar at various addition rates (0 %, 0.5 %, 1 %, 2 %, 3 %, and 5 %) on wetting peak migration, cumulative infiltration, water absorption and retention, and N leaching. The results showed that, compared with bulk biochar, nano-biochar presented a more abundant pore structure with an increase in specific surface area of approximately 1.5 times, accompanied by a 20 % increase in acid functional groups. Compared with those for clayey soil without biochar addition, the wetting front migration time was increased by 10.2 %-123.9 % and 17.0 %-257.9 %, and the cumulative infiltration volume at 60 min was decreased by 26.0 %-48.4 % and 14.1 %-62.4 % for bulk biochar and nano-biochar, respectively. The parameter S of Philip model and the parameter a of Kostiakov model for nano-biochar were lower than those for bulk biochar, whereas the parameter b of Kostiakov model was greater, indicating that nano-biochar decreased initial soil infiltration rate and increased attenuation degree of the infiltration rate. Nano-biochar increased water absorption by 8.03 % and subsequently enhanced water retention capacity relative to bulk biochar. In addition, bulk biochar and nano-biochar reduced NH4+-N leaching by 3.0 %-13.1 % and 5.7 %-39.2 %, respectively, and NO3--N leaching by 2.7 %-3.6 % and 9.0 %-43.3 %, respectively, by decreasing N concentration and leachate volume relative to those with no biochar addition. This study provides new knowledge for nano-biochar application in a clayey soil.

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