Effects of aridification on soil total carbon pools in China's drylands

From soil to the intestinal tract: The key role of beneficial elements and probiotics in promoting health and longevity

Although soil quality and gut probiotics have been extensively accepted as critical for human health, the combined effects of soil and fecal bacteria on public health remain underexplored. This study collected soil and human fecal samples from three towns with high, medium, and low proportion of longevous populations in a well-known longevity region in Yangtze River Delta, China. Beneficial elements were detected in all soils, including selenium (0.01-0.05 mg kg-1), germanium (1.07-1.44 mg kg-1), boron (0.42-1.49 mg kg-1), zinc (1.07-1.70 mg kg-1) and manganese (38.78-43.52 mg kg-1). These elements were more abundant in high-proportion region (HP) compared to medium (MP) and low (LP) proportion region (p < 0.05). Similar dominant bacteria were detected in all soils and feces, including Proteobacteria (29.93 %), Acidobacteriota (16.23 %), and Bacillus (2.25 %). Notably, positive correlations were detected between beneficial metal contents and soil bacterial abundance (p < 0.05), suggesting a role in promoting bacterial growth. Moreover, beneficial element metabolic genes, such as zupT (encoding high-affinity zinc transporter for active zinc ion transport) and mntA (encoding manganese ion transporter protein) were significantly enriched in HP soil and fecal bacteria (p < 0.05). Additionally, Source Tracker analysis indicated that 41.13 % of fecal bacteria in HP area originated from HP soil bacteria. Structural equation model indicated that soil beneficial elements significantly enhanced the relative abundance of probiotic associated genes in the dominant fecal bacteria (path coefficients of 0.869 and 0.905, respectively; p < 0.05). Together, soil-borne beneficial elements promote intestinal bacterial functionality, contributing to human health and longevity.

Restoration type determines synchronic recovery of soil carbon, nitrogen, and phosphorus in mangrove wetlands

Restoration is essential for preserving the functions and economic benefits of mangrove ecosystems. Soil organic carbon (SOC), total nitrogen (TN), and total phosphorus (TP) can help assess restoration effectiveness. However, it remains unclear whether active restoration (AR) with planting better recovers these nutrients than passive restoration (PR) without planting. We measured SOC, TN, and TP in four soil layers (0-10, 10-20, 20-30, and 30-40 cm) in experimental plots restored using AR and PR pond-to-mangrove methods over three years. The trials were compared to nearby natural mangrove forests in the Qinglan Harbor area of Hainan Island, China. We found that the SOC, TN, and TP contents in restored mangroves were significantly lower than those in natural mangroves, highlighting the long-term nature of ecosystem recovery. However, no significant differences were observed in SOC (10.40 ± 0.71 vs. 8.95 ± 0.54 g kg-1), TN (0.47 ± 0.04 vs. 0.44 ± 0.03 g kg-1), and TP (0.14 ± 0.01 vs. 0.09 ± 0.01 g kg-1) contents between AR and PR sites. This challenges the common assumption that AR is always superior to PR. The scaling slopes of the C:N:P stoichiometric relationships remained consistent (slope = 1) across the whole study area and at each site and soil depth, indicating tight coupling of these elements post-restoration. Soil salinity and bacterial community richness were identified as significant determinants of nutrient levels. Our findings suggest that both AR and PR are viable restoration options, depending on ecological needs, economic resources, and sustainability goals.

Sand barriers promote the accumulation of soil nutrients in sandy areas under different ecological conditions: A meta-analysis

Sand barriers have been widely employed in projects aimed at stabilizing moving sand. Their construction directly influences the comprehensive dynamics of wind speed and sediment deposition. However, there is limited understanding of the magnitude of soil nutrients responses to sand barriers and the effects of various driving factors. This study collected data from 43 studies, encompassing 951 observations. Using meta-analysis, we investigated the effects of sand barriers on soil nutrients and analyzed the regulatory effects of ecological factors and sand barrier properties on soil nutrients. The results show that sand barriers significantly increased the accumulation of soil organic carbon (p < 0.01), total nitrogen (p < 0.01), available nitrogen (p < 0.01), total phosphorus (p < 0.01), and available phosphorus (p < 0.01). Among them, the regulation effect on total nitrogen was the most notable, with 67 % increase. Moreover, combined sand barriers integrating mechanical and vegetative measures better promoted soil nutrients, particularly in enhancing soil phosphorus, with total phosphorus increasing by 36 % and available phosphorus increasing by 52 %. These results suggested that combining these measures can maximize the protective effectiveness. Furthermore, under conditions of water scarcity, ecological factors exerted a more significant effect on regulating soil nutrients than sand barrier properties. The mean annual precipitation (MAP) is the most critical factor among considered ecological indicators - soil sampling depth, altitude, the mean annual wind speed, MAP, the mean annual temperature, and the mean annual evaporation. Taken together, these results suggested that sand barriers installation has a positive effect on soil nutrient accumulation in sandy areas, providing scientific support for desertification control and sustainable land management.

Mapping Soil Organic Carbon by Integrating Time-Series Sentinel-2 Data, Environmental Covariates and Multiple Ensemble Models

Despite extensive use of Sentinel-2 (S-2) data for mapping soil organic carbon (SOC), how to fully mine the potential of time-series S-2 data still remains unclear. To fill this gap, this study introduced an innovative approach for mining time-series data. Using 200 top soil organic carbon samples as an example, we revealed temporal variation patterns in the correlation between SOC and time-series S-2 data and subsequently identified the optimal monitoring time window for SOC. The integration of environmental covariates with multiple ensemble models enabled precise mapping of SOC in the arid region of southern Xinjiang, China (6109 km2). Our results indicated the following: (a) the correlation between SOC and time-series S-2 data exhibited both interannual and monthly variations, while July to August is the optimal monitoring time window for SOC; (b) adding soil properties and S-2 texture information could greatly improve the accuracy of SOC prediction models. Soil properties and S-2 texture information contribute 8.85% and 61.78% to the best model, respectively; (c) among different ensemble models, the stacking ensemble model outperformed both the weight averaging and sample averaging ensemble models in terms of prediction performance. Therefore, our study proved that mining spectral and texture information from the optimal monitoring time window, integrated with environmental covariates and ensemble models, has a high potential for accurate SOC mapping.

Nonlinear influences of climatic, vegetative, geographic and soil factors on soil water use efficiency of global karst landscapes: Insights from explainable machine learning

Soil Water Use Efficiency (SWUE) represents a vital metric for assessing the relationship between carbon acquisition and soil moisture (SM) depletion in terrestrial ecosystems. However, the elucidation of time-lagged and cumulative effects, nonlinear influences, and indirect contributions of explanatory variables, including climate and vegetation characteristics, on SWUE in global karst landscapes remains limited. In this study, we analyzed the time-lagged and cumulative effects of climatic and biological factors on SWUE in global karst landscapes using the Autoregressive Distributed Lag Model. By comparing nine machine learning models, we further revealed the nonlinear effects, as well as the direct and indirect contributions of climatic, geographic, soil, and biological explanatory variables on SWUE across varying aridity, using the Random Forest Model, SHapley Additive exPlanations, Generalized Additive Model, and Partial Least Squares-Structural Equation Modeling (PLS-SEM). The findings suggested that precipitation and wind speed exert the most substantial time-lagged and cumulative impacts on SWUE in global karst landscapes, respectively. The Random Forest model outperforms eight other machine learning models, including CatBoost, LightGBM, and XGBoost, in accurately simulating SWUE. In global karst landscapes, SWUE was significantly affected by the positive contributions of evapotranspiration, leaf area index, and temperature, as well as the negative impacts of latitude and longitude. These influences exhibited varying degrees of nonlinearity across the aridity gradient. Using PLS-SEM based on the 'geo-climatic-soil-biological' cascade effect, it was found that gross primary production directly and significantly influences karst SWUE under both drought-prone and water-abundant conditions, significantly exceeding the impact of SM. Geographic, climatic, and biological factors indirectly influenced karst SWUE by affecting gross primary production. The impact of soil type, soil carbon and nitrogen content, and rootable depth on SWUE was minimal. This study enhances our understanding of carbon sinks and the water‑carbon cycle, providing valuable insights into resource use efficiency within karst environments.

Exploring the spatial heterogeneity of soil organic carbon and the influence of coastal factors: A case study in the Yellow River Delta, China

Terrestrial ecosystems have vital impacts on soil carbon sequestration, but under disturbances from anthropogenic activities, the typical indicator combinations of SOC distribution in coastal areas remain unclear. On the basis of surface soil sampling and calculations of related eco-environmental indices in the Yellow River Delta (YRD), we performed geostatistical analysis combined with Spearman's correlation analysis, principal component analysis (PCA), and hierarchical clustering analysis (HCA) to explore the spatial heterogeneity of soil organic carbon (SOC) and influential spatiotemporal factors. Overall, the results revealed that in the seaward direction of the Yellow River, the SOC concentration decreased from west to east, with a low mean value of 5.57 g·kg-1. We selected nine indicators that significantly influenced the SOC distribution among four types of coastal factors, namely, land cover, soil components, geographical conditions and anthropogenic activities. On the basis of these results, potential anthropogenic interventions that can increase SOC sequestration are presented: the coverage of saline-alkali-tolerant plant types should be increased, especially in bare areas on the east coast and in saline-alkali land, forests, and grassland, and soil fertility in agricultural areas should be maintained to improve the carbon sequestration capacity of surface vegetation. Herein, we present new insights for exploring the dynamic impacts of ecosystem factors on terrestrial soil carbon and present targeted sequestration strategies in areas with intense sea-land interactions.

Ecological restoration enhances dryland carbon stock by reducing surface soil carbon loss due to wind erosion

Enhancing terrestrial carbon (C) stock through ecological restoration, one of the prominent approaches for natural climate solutions, is conventionally considered to be achieved through an ecological pathway, i.e., increased plant C uptake. By conducting a comprehensive regional survey of 4279 1 × 1 m2 plots at 517 sites across China's drylands and a 13-y manipulative experiment in a semiarid grassland within the same region, we show that greater soil and ecosystem C stocks in restored than degraded lands result predominantly from decreased surface soil C loss via suppressed wind erosion. This biophysical pathway is always overlooked in model evaluation of land-based C mitigation strategies. Surprisingly, stimulated plant growth plays a minor role in regulating C stocks under ecological restoration. In addition, the overall enhancement of C stocks in the restored lands increases with both initial degradation intensity and restoration duration. At the national scale, the rate of soil C accumulation (7.87 Tg C y-1) due to reduced wind erosion and surface soil C loss under dryland restoration is equal to 38.8% of afforestation and 56.2% of forest protection in China. Incorporating this unique but largely missed biophysical C-conserving mechanism into land surface models will greatly improve global assessments of the potential of land restoration for mitigating climate change.

Dynamic Responses of Soil Organic Carbon to Urbanization: A Global Perspective

Rapid global urbanization has a complex impact on soil organic carbon (SOC) stocks. Through its direct and indirect impacts on soil formation and development, urbanization greatly influences SOC stocks. However, the extent to which urbanization affects SOC stocks globally remains unclear. In this study, we utilized an urban-rural gradient approach to assess the effects of urbanization on SOC stocks at both global and national scales. First, we calculated the urbanization intensity (UI) at a 1 km scale globally, categorizing urbanization into three stages: low (0 ≤ UI ≤ 25), medium (25 < UI ≤ 75), and high (75 < UI ≤ 100). Additionally, we distinguished the contributions of natural factors and human activities and analyzed the effects of land-use changes in eight representative cities. We found the following: (1) The SOC stocks exhibit distinct trends with increasing UI, but when UI is low or high, an increase in UI is associated with decreasing SOC stocks (reductions of 6.8% and 5.4% at a depth of 30 cm; 6.4% and 3.2% at a depth of 100 cm, respectively). (2) Changes in human activities are the main drivers of SOC stock changes during urbanization. At low and medium urban intensities, the contributions of human activities reach 98% and 89%, respectively. Additionally, land-use transitions are closely correlated with SOC stock changes, particularly in areas near the urban core, across different climate zones. (3) The response of SOC to urbanization varies across climatic zones. In water-scarce arid climates, attention should be given to the negative effects of urbanization, and more targeted measures should be taken to enhance the carbon sequestration capacity of urban soils. This study provides valuable insights into the dynamic interplay between urbanization and SOC stocks, underscoring the need for tailored strategies to manage soil carbon in urban environments.

Inorganic Carbon Pools and Their Drivers in Grassland and Desert Soils

Inorganic carbon is an important component of soil carbon stocks, exerting a profound influence on climate change and ecosystem functioning. Drylands account for approximately 80% of the global soil inorganic carbon (SIC) pool within the top 200 cm. Despite its paramount importance, the components of SIC and their contributions to CO2 fluxes have been largely overlooked, resulting in notable gaps in understanding its distribution, composition, and responses to environmental factors across ecosystems, especially in deserts and temperate grasslands. Utilizing a dataset of 6011 samples from 173 sites across 224 million hectares, the data revealed that deserts and grasslands in northwestern China contain 20 ± 2.5 and 5 ± 1.3 petagrams of SIC in the top 100 cm, representing 5.5 and 0.76 times the corresponding soil organic carbon stock, respectively. Pedogenic carbonates (PIC), formed by the dissolution and re-precipitation of carbonates, dominated in grasslands, accounting for 60% of SIC with an area-weighted density of 3.4 ± 0.4 kg C m-2 at 0-100 cm depth, while lithogenic carbonates (LIC), inherited from soil parent materials, prevailed in deserts, constituting 55% of SIC with an area-weighted density of 7.1 ± 1.0 kg C m-2. Soil parent materials and elevation determined the SIC stocks by regulating the formation and loss of LIC in deserts, whereas natural acidification, mainly induced by rhizosphere processes including cation uptake and H+ release as well as precipitation, reduced SIC (mainly by PIC) in grasslands. Overall, the massive SIC pool underscores its irreplaceable role in maintaining the total carbon pool in drylands. This study sheds light on LIC and PIC and highlights the critical impact of natural acidification on SIC loss in grasslands.

Biodegradable Microplastic-Driven Change in Soil pH Affects Soybean Rhizosphere Microbial N Transformation Processes

The potential impacts of biodegradable and nonbiodegradable microplastics (MPs) on rhizosphere microbial nitrogen (N) transformation processes remain ambiguous. Here, we systematically investigated how biodegradable (polybutylene succinate, PBS) MPs and nonbiodegradable (polyethylene, PE) MPs affect microbial N processes by determining rhizosphere soil indicators of typical Glycine max (soybean)-soil (i.e., red and brown soils) systems. Our results show that MPs altered soil pH and dissolved organic carbon in MP/soil type-dependent manners. Notably, soybean growth displayed greater sensitivity to 1% (w/w) PBS MP exposure in red soil than that in brown soil since 1% PBS acidified the red soil and impeded nutrient uptake by plants. In the rhizosphere, 1% PBS negatively impacted microbial community composition and diversity, weakened microbial N processes (mainly denitrification and ammonification), and disrupted rhizosphere metabolism. Overall, it is suggested that biodegradable MPs, compared to nonbiodegradable MPs, can more significantly influence the ecological function of the plant-soil system.

Changes of soil carbon along precipitation gradients in three typical vegetation types in the Alxa desert region, China

The changes and influencing factors of soil inorganic carbon (SIC) and organic carbon (SOC) on precipitation gradients are crucial for predicting and evaluating carbon storage changes at the regional scale. However, people's understanding of the distribution characteristics of SOC and SIC reserves on regional precipitation gradients is insufficient, and the main environmental variables that affect SOC and SIC changes are also not well understood. Therefore, this study focuses on the Alxa region and selects five regions covered by three typical desert vegetation types, Zygophyllum xanthoxylon (ZX), Nitraria tangutorum (NT), and Reaumuria songarica (RS), along the climate transect where precipitation gradually increases. The study analyzes and discusses the variation characteristics of SOC and SIC under different vegetation and precipitation conditions. The results indicate that both SOC and SIC increase with the increase of precipitation, and the increase in SOC is greater with the increase of precipitation. The average SOC content in the 0-300cm profile is NT (4.13 g kg-1) > RS (3.61 g kg-1) > ZX (3.57 g kg-1); The average value of SIC content is: RS (5.78 g kg-1) > NT (5.11 g kg-1) > ZX (5.02 g kg-1). Overall, the multi-annual average precipitation (MAP) in the Alxa region is the most important environmental factor affecting SIC and SOC.

Shifts in plant functional groups along an aridity gradient in a tropical dry forest

Increasing aridity associated with climate change may lead to the crossing of critical ecosystem thresholds in drylands, compromising ecosystem services for millions of people. In this context, finding tools to detect at early stages the effects of increasing aridity on ecosystems is extremely urgent to avoid irreversible damage. Here, we assess shifts in plant community functional structure along a spatial aridity gradient in tropical dryland (Brazilian Caatinga), to select the most appropriate plant functional groups as ecological indicators likely useful to predict temporal ecosystem trajectories in response to aridity. We identified seven plant functional groups based on 13 functional traits associated with plant establishment, defense, regeneration, and dispersal, whose relative abundances changed, linearly and non-linearly, with increasing aridity, showing either increasing or decreasing trends. Of particular importance is the increase in abundance of plants with high chemical defense and Crassulacean Acid Metabolism (CAM) photosynthetic pathway, with increasing aridity. We propose the use of these functional groups as early warning indicators to detect aridity impacts on these dryland ecosystems and shifts in ecosystem functioning. This information can also be used in the elaboration of mitigation and ecological restoration measures to prevent and revert current and future climate change impacts on tropical dry forests.