Unraveling the drivers and synergistic mechanisms of selenium distribution in cultivated soils across China: A...

Selenium (Se) is an essential yet potentially toxic micronutrient for human health, and its distribution in cultivated soils is fundamentally linked to ecosystem safety. This study evaluated the spatial distribution of Se in China's surface cultivated soils by integrating a reviewed database with field surveys. Using random forest-Shapley additive explanations and structural equation modeling, we analyzed 22 environmental factors to identify the dominant drivers and their interactive mechanisms. The results showed that the mean Se content of cultivated soil in China was 0.283 mg·kg^-1, with a coefficient of variation of 51.6%. Although the classic spatial pattern persists, Se-sufficient and Se-rich soils have expanded markedly, covering 55.6% and 19.8% of the total area, respectively. Mean annual precipitation (MAP), aridity index (AI), net primary productivity (NPP), and evapotranspiration (ET) emerged as the primary determinants, confirming the predominant role of climate at the national scale. Notably, substantial interaction effects were observed between ≥ 0℃ accumulative temperature (ATT0) and MAP, and between ATT0 and AI, highlighting that hydrothermal interactions exert primary control on soil Se distribution. Additional climate-soil couplings, specifically AI with pH, and AI with cation exchange capacity (CEC), further reinforced this spatial differentiation. Furthermore, NPP served as a key biogeochemical intermediary, with its biologically driven pathway exerting a greater total effect on soil Se than that mediated by soil properties. This work provides quantitative evidence of the key drivers shaping Se distribution in cultivated topsoils across China and offers practical guidance for the sustainable soil Se management and public nutritional health protection.