Drivers for changes in ecosystem multifunctionality in China under different soil pH conditions

In recent years, soil acidification has been expanding in many areas of Asia due to increasing reactive nitrogen inputs and industrial activities, which may seriously affect the performance of various ecosystem functions. However, the underlying patterns and processes of ecosystem multifunctionality (EMF) are largely unknown at different levels of pH, limiting our understanding of how EMF respond to drivers. This study aims to explore threshold of pH on changes in EMF and differences in the drivers for the changes in EMF on either side of each of the determined pH thresholds. We collected nutrient and environmental databases for raster-level sampling data, totaling 4, 000 sampling points. Averaging and cluster-multiple-threshold approach were used to calculate EMF, then quadratic and generalized additive models and Mann-Whitney U were used to determine and test the pH thresholds for changes in EMF, structural equation modellings and variance partitioning analysis were used to explore the main drivers on changes in EMF. The pH threshold for EMF changes in Chinese terrestrial ecosystems is 6.0. When pH < 6.0, climate was consistently more important in controlling the variation of EMF than other variables; when pH ≥ 6.0, soil was consistently more important in controlling the variation of EMF than other variables. Specifically, when pH < 6.0, mean annual temperature was the main factor in regulating the EMF variation; when pH ≥ 6.0, soil moisture was the main factor in regulating the EMF variation. Our study provides important scientific value for the mechanism of maintaining EMF under global change. For example, with further increases in global nitrogen deposition, leading to increased soil acidification, there are different impacts on EMF in different regions. It may lead to a decrease in EMF in acidic soils and an increase in EMF in alkaline soils. This suggests different management strategies for different regions to maintain EMF stability in the context of future global changes. In the future, more attention should be paid to the biological mechanisms regulating EMF.