Identifying the ecological risk patterns and the dominant ecological risks for ecosystems is crucial for optimizing regional ecological environment quality and formulating sustainable socioeconomic development polices. We established an ecological risk assessment (ERA) model for the Wuling Mountain region to identify the dominant ecological risks in the region and analyzed the constraint effects of the influencing factors on the ecological risk. The results indicated that the relatively high-risk areas were mainly distributed in the northeastern and western regions, along with scattered areas of high risk. The area which had dominant ecological risks was 89,500 km 2, accounting for 52.14% of the total area. Meanwhile, the regions with higher ecological risks had multiple dominant risk types. Among all influencing factors, NPP, population density (POP) and temperature (TMP) were highlighted as key factors affecting ecological risk, with an explanatory power consistently exceeding 0.20. There were three types of constraint effects of influencing factors on ecological risk, including logarithmic, negative convex and hump-shaped. Thresholds occurred for the constraint lines of TMP, precipitation (PRE), evapotranspiration (EVA), NPP, elevation (DEM) and slope (SLO), respectively, indicating that the stressors influencing ecological risk vary on either side of these thresholds. This finding is significant for policy formulation, as it allows for prioritization of adjustments based on the explanatory power and the magnitude of these threshold values. Overall, the results of this study provide a comprehensive regulatory framework and regionally targeted scientific support for ecological protection and restoration in the Wuling Mountain region.

Biochar is suggested as a soil amendment to improve salt-affected soil properties for crop productivity and decrease soil salinity. However, the heterogeneity among biochar experiments in terms of biochar and soil properties and experimental conditions makes it difficult to compare and extrapolate results from different studies. A statistical meta-analysis was undertaken with the aim of evaluating the impacts of biochar on crop productivity and soil salinity in salt-affected soils. The results showed a statistically significant benefit of biochar application to salt-affected soils on crop productivity. The application rate of 40-50 t/ha (41%), C/N ratio of 40-60 (33%), pyrolysis temperature of 450-550 °C (28%) and pH of 7-8 (30%) of biochar yielded the greatest (positive) effects on crop productivity and did not cause an increase in soil salinity in salt-affected soil. With regard to climate analyses, biochar application had the greatest (positive) effects on crop productivity and the greatest (negative) effects on soil salinity at mean annual temperature (MAT) <10 °C (30%), mean annual precipitation (MAP) <400 mm (33%) and MAT <10 °C (-9%), MAP< 400 mm (-9%), respectively. This suggests that the crop productivity increase may be due to an improvement in soil temperature and water retention and a decrease in soil salinity. The greater (positive) effects on crop productivity with regard to soil analyses were seen at pH >8 (24% to 25%), salinity >5 (32% to 60%), and sulfate-dominated (35%) and soda-dominated (26%) saline soils. The greater (negative) effects on soil salinity with regard to soil analyses were seen at salinity >5 (-9% to 22%), and sulfate-dominated (-35%) and soda-dominated (16%) saline soils. This suggests that the crop productivity increase may be due to a decrease in soil pH and salinity in sulfate-dominated or soda-dominated saline soils. A statistically significant increase in the productivity of cash crops and rice was found in salt-affected soils treated with biochar, but soil salinity also increased. A statistically significant increase in crop productivity by biochar was seen in the salt-affected soils with the addition of inorganic fertilizer and no fertilizer compared to the absence of biochar. This meta-analysis provides the first quantitative review of the effect of biochar on crop productivity and soil salinity in salt-affected soil, which is critical for developing engineered biochar to restore salt-affected soil and promote food security.