Ecological risk changes and their relationship with exposed surface fraction in the karst region of southern China from 1990 to 2020

Nano-selenium modified green eggshell biochar reduces cadmium accumulation in shallots (Allium schoenoprasum L.)

Green eggshell biochar, a renewable biomass material, demonstrates promising potential for environmental remediation. This study systematically prepared biochar under varying pyrolysis conditions and identified nano-selenium-modified biochar (produced at 600 °C for 3 h, termed 6-3 S) as the optimal formulation for cadmium (Cd) immobilization. Compared to untreated soil, the 6-3 S biochar reduced bioavailable Cd content by 38.65 % in contaminated soil. Correspondingly, Cd accumulation in shallot tissues decreased by 56.64 % (white parts) and 82.69 % (green parts). Furthermore, the 6-3 S treatment enhanced plant selenium levels by 21.3-29.8 % and preserved leaf microstructure integrity, reducing stomatal deformation by 44.2 % compared to controls. Additionally, Nitro Blue Tetrazolium (NBT) staining area decreased from 39.03 % to 24.00 %, indicating reduced oxidative stress. These dual effects-Cd suppression and selenium enrichment-significantly improved shallot quality and safety. The findings establish a scientific foundation for deploying nano-selenium-modified biochar in heavy metal-contaminated agricultural systems.

Relative forces of anthropogenic and natural factors on the evolution of "ecological cancer"-rocky desertification under different man-land relationships

Rocky desertification (RD) is a severe phenomenon in karst areas, often referred to as "ecological cancer." However, studies on RD rarely include comparative analysis of different man-land relationship areas. This lack of analysis leads to difficulties in preventing and controlling RD in local areas with complex man-land relationships. To address this issue, we selected two typical karst areas, Guangnan County (with subtropical humid and agricultural peak-valley area) and Yulong County (with temperate semi-arid and ecological tourism alpine-canyon area), as comparative research areas. We analyzed the evolution of RD in these two typical areas and revealed the relative forces of anthropogenic and natural factors on RD at both a single and comprehensive level by using the geographical detector and the coupled principal component-structural equation model. The study found that (1) the RD in Yulong County was more severe than that in Guangnan County. From 2010 to 2020, RD in both counties showed a positive succession trends. The RD has a high degree of spatial fragmentation, and spatial evolution usually occurs in areas where the man-land relationship is complex. (2) In terms of single factor, the RD in the two counties was mainly affected by anthropogenic factors such as control, farming, behavioral disturbance, and social economy, and natural factors such as geology, soil, topography, and surface state. (3) Comprehensive effects show that forces of anthropogenic vs natural factors on formation/evolution of RD are different between Guangnan County (0.36 for anthropogenic factor vs -0.64 for natural factor) and Yulong County (higher with anthropogenic: 0.44 vs natural: 0.89). (4) Differentiated strategies should be adopted due to role played by anthropogenic and natural factors across different man-land relationship areas to explore suitable control measures for RD. The research creates a scientific basis for the control of RD, ecological restoration, and sustainable development in various regions. It can also be utilized as a valuable reference for comparative analysis of similar geographical phenomena.

Spatial heterogeneity of soil properties in planted mixed forests in the rocky desertification areas of the Wuling Mountain

In this study, experiments were conducted on soil samples collected from depths of 0-15 cm, 15-30 cm, and 30-50 cm at the National Long-term Scientific Research Base for the Comprehensive Management of Rocky Desertification in the Wuling Mountains. The aim was to determine the physicochemical indexes and explore the nature and spatial heterogeneity of the soil of the planted mixed forests within the rocky desertification area of the Wuling Mountain. Various analytical methods were employed, including descriptive statistical analysis, correlation analysis, analysis of variance, principal component analysis, spatial interpolation analysis, and kriging interpolation, to fit the optimal model of the semi-variance function of soil physicochemical properties and analyze the model's parameters. The results indicated that soil physical and chemical properties varied with depth and were generally correlated. The relationship between soil organic matter and total nitrogen content was the closest. Additionally, there was a certain degree of correlation between soils at different depths in the vertical profile, generally the correlation between layer B (15-30 cm) and layer C (30-50 cm) > that between layer A (0-15 cm) and layer B (15-30 cm) > that between layer A (0-15 cm) and layer C (30-50 cm). The weighting coefficients of the principal components of soil physicochemical properties indicated that soil organic matter, nitrogen, phosphorus, potassium, pH, total porosity, and capillary porosity are key factors in the soil properties of karst desertification areas. The spatial variability of soil physicochemical properties at different depths ranged from 21.91 to 87.59 m, and the abutment ratio (Co/Co+C) of these properties ranged from 12.99% to 89.53%. Using kriging interpolation in ArcGIS, the spatial distribution pattern of soil physical and chemical properties was mapped, revealing that these indicators were distributed with heterogeneous patches of various sizes and shapes. Therefore, the degree of rocky desertification significantly influences the spatial distribution pattern of soil physical and chemical properties.

Intricate synergistic effects between air pollution and carbon emission: An emerging evidence from China

Due to global climate change and intensifying anthropogenic pollution, China confronts the dual challenge of controlling particulate matter 2.5 μm (PM2.5) pollution and reducing carbon emissions. Quantifying the characteristics of PM2.5 concentrations and CO2 emissions, as well as identifying the driving factors and synergistic effects of PM2.5 reduction and CO2 mitigation, are crucial steps in promoting sustainable urban development and achieving the Sustainable Development Goals (SDGs) in China. In this study, we selected 168 cities as our case-study, and quantified spatial characteristics of PM2.5 concentrations and CO2 emissions from 2015 to 2020 in China. Then we analyzed driving factors affecting the spatial heterogeneity of PM2.5 reduction and CO2 mitigation applying Multi-scale Geographically Weighted Regression (MGWR) model. By employing coupling coordination degree (CCD) model, we further detected the spatiotemporal evolution patterns of the synergistic effects between PM2.5 reduction and CO2 mitigation in key Chinese cities. The result showed that: (a) From 2015 to 2020, PM2.5 concentrations experienced a significant reduction from 59.78 μg/m3 to 49.83 μg/m3, while CO2 emissions increased from 44.88 × 106 t in 2015 to 45.77 × 106 t in 2020; (b) Green economy efficiency (gee), government attention (gover), and environmental regulation (envir) demonstrate the most pronounced synergistic effect on pollution reduction and carbon mitigation, with the drivers exhibiting obvious spatial heterogeneity; (c) The overall coupling coordination level of PM2.5 pollution and CO2 emissions in China dropped from 0.49 in 2015 to 0.46 in 2020, and the coupling coordination grade in northern cities was notably higher than that in southern cities. The result enhances our understanding of spatiotemporal patterns of synergistic effects between PM2.5 reduction and CO2 mitigation, and provides the theoretical basis for policy decision-making to realize pollution decrease and carbon neutral and regional environment governance.

Exploring watershed ecological risk bundles based on ecosystem services: A case study of Shanxi Province, China

Humans are having an increasingly profound impact on the environment along with the advent of the Anthropocene. Ecological risk assessment (ERA) as a method to quantify ecological problems can provide support for decision-makers, and it is one of key issues to integrate ecosystem services into ERA. In this study, an ERA framework was proposed under the loss-probability paradigm from the perspective of ecosystem services risk bundles. The results showed that initiatives aimed at ecological protection in Shanxi Province had been effective, the number of watersheds with low-risk bundles increased significantly (from 16.09% to 34.49%) and the watersheds basically overlapped with key forestation areas. However, the effects of forestation activities may no longer be as significant as they once were, as the relationship between forestation and water supply was becoming increasingly contradictory. Meanwhile, the conflict between urban expansion and natural ecosystem protection was intensifying, habitat degradation risks were gradually polarized, and the risk bundles dominated by high carbon emission and habitat degradation were increasing significantly (from 15.88% to 33.54%). Strengthening the construction of urban green space and controlling the expansion of human activities may be the next focus of ecological conservation in Shanxi Province. This study enriched the ERA framework with an ecosystem services risk bundle approach.

Effectiveness and driving mechanism of ecological restoration efforts in China from 2009 to 2019

Over the past decades, China's rapid economic growth and industrialization have led to serious ecological concerns. To combat ecological degradation and promote ecosystem sustainability, China has made substantial investments in ecological restoration in recent decades. Nevertheless, a comprehensive analysis of the effectiveness and driving mechanisms of these efforts are still lacking. Therefore, this study aims to bridge this gap by employing national land-use survey data to evaluate the effectiveness and driving mechanisms of China's ecological restoration efforts during 2009-2019, with a specific focus on ecological land preservation, land use structure, and their contribution to ecosystem services. Additionally, the Geodetector model was used to detect potential influencing factors and driving mechanisms of these efforts. The results of this study revealed that: (1) Between 2009 and 2019, a total of 585,492.61 km2 of non-ecological land was successfully transformed into ecological land through various ecological restoration efforts. Most of these areas were previously unused or cultivated land. (2) Forest and grass plantations were the major ecological restoration efforts in China, accounting for 47.35% and 41.91% of the total restored ecological land, respectively. Grassland restoration clustered northwest of the Hu Line, while forest restoration concentrated mainly to the southeast. Water and wetlands restoration were mainly distributed around China's major rivers, such as the Yangtze River and Yellow River. (3) China's ecological restoration efforts contributed to a 2.53 trillion CNY yuan increase in ecosystem service value during 2009-2019, with over 65% of the increase attributed to ecosystem regulating services. (4) China's ecological restoration efforts were mainly influenced by anthropogenic factors, such as population, land use, and urbanization, while the non-linearly enhanced interaction between natural and other factors also deserves attention. China should balance urban expansion, agricultural development, and ecological preservation, aligning restoration with socioeconomic trends while establishing effective inter-regional ecological compensation mechanisms.

Ecological Stoichiometry and Stock Distribution of C, N, and P in Three Forest Types in a Karst Region of China

Ecological stoichiometry plays important roles in understanding the nutrient constraints on tree growth and development, as well in maintaining ecosystem services in forests, yet the characteristics of carbon:nitrogen:phosphorous (C:N:P) stoichiometry in forests under karst environment have not been sufficiently evaluated. In this study, concentration, distribution, stocks of Nitrogen (N) and Phosphorous (P), and ecological stoichiometry were studied in three common forest types: Masson pine natural forests (MPNF), Masson pine plantation forests (MPPF), and Slash pine plantation forests (SPPF) in a karst region of southwestern China. Results showed that N concentrations were higher in overstory than in understory and litter in the studied forests. However, P concentration was relatively low in overstory component of the forested ecosystems. Meanwhile, the N and P concentrations were higher in SPPF in the stem and litter, while these contents were higher in MPPF and MPNP in the overstory and understory. The N and P stocks ranged from 5.7-6.2 t ha^-1, and 0.5-0.6 t ha^-1 in the examined forests. The ecological stoichiometry of C:N:P in the three forest types was similar in litter (46-49:2:1), and relatively steady in soil (250-320:13-16:1) and tree leaf (100-200:14-20:1). Soil P status was the primary limiting factor in affecting tree growth in MPPF and SPPF (N:P ratio > 16), while both N and P conditions were the main restrictive factors in MPNP (N:P ratio = 15) in the study area. Our study provides scientific references and useful datasets of C:N:P stoichiometry for sustainable management of forest ecosystems in karst regions.