No abstract

To explore whether and how anthropogenic activities related to surface water regulation (i.e., dam construction) disturb soil ecosystems in the surrounding uplands, a long-term monitoring program was conducted from 1998 to 2017 in the Three Gorges Reservoir Region, China. The Three Gorges Dam (TGD) is the largest hydraulic engineering project in the world. We present a direct, ecosystem-scale demonstration of changes in the soil organic carbon (SOC) content in the TGD watershed before and after the surface water was reshaped. The average SOC content decreased from 12.9 to 9.5 g/kg between 2004 and 2012 and then recovered to 13.8 g/kg in 2017. Dynamics of SOC were partly attributed to shifts in the composition of soil microbial communities responsible for carbon biogeochemistry. The shifts in microbial taxa were associated with the changed microclimate affected by the TGD as well as global and regional climate variability. The microclimate, soil microorganisms, and plant organic carbon input explained 40.2% of the variation in the SOC content. This study revealed that dam construction was an important and indirect driver for the SOC turnover, and the subsequent effects on the upland soil ecosystem must be considered when large-scale disturbance activities (such as dam construction) are conducted in the future.

The increasing need for citrus has driven the rapid expansion of citrus planting areas. However, not all areas are suitable for growing citrus. It is necessary to understand the future changing trend of environmental suitability in citrus-producing areas. Here, based on the soil nutrient data of citrus cultivation from 2006 to 2018, the spatiotemporal kriging method was used to predict the spatiotemporal distribution of soil nutrients in Zigui County, Hubei Province. Then, geographical and meteorological conditions were combined to evaluate the suitability for citrus cultivation at temporal and spatial levels, and the results were verified by the yield and quality data of citrus. The results showed that from 2018 to 2027, the overall suitability of the citrus-producing area displayed a gradually rising trend, with the “suitable” producing area increasing from 4.5% to 20.16%. The validation results indicated that the mean relative errors of spatiotemporal predictors were less than 30% except for the effective iron. Correlation analysis revealed that the proportion of “moderately suitable” and “suitable” orchards had significant positive correlations with annual yield. The low suitability of Maoping town was mainly attributed to its soil acidification and available P content, and that of Shazhenxi town was ascribed to its low soil contents of available P and N. The optimal fertilization scheme was constructed by an artificial neural network to optimize the fertilization status of some citrus producing areas. This study has created a dynamic assessment of the environmental suitability of citrus production areas to support improvements in citrus production.