Socioeconomic gradients modulate climate and soil controls on plant functional traits across China

Understanding how socioeconomic development modulates trait–environment linkages in the Anthropocene, particularly its mechanistic role in reshaping the relative importance of climate versus soil drivers, remains poorly understood. We used county-level GDP as a proxy for human ecological activities, reflecting regional differences in land-use and management, and treated it as a moderator that indirectly alters plant responses to climate and soil drivers via human activities. Using 25,624 vascular plant species across China, we examined whether a county-level GDP alters (rather than replaces) climate–soil controls on four key traits: leaf area, maximum plant height, seed size, and cone size. We first used generalized additive models and segmented regressions to detect nonlinearities and GDP thresholds in trait responses, then applied random forests with SHAP to quantify driver importance, and finally used structural equation models to test indirect pathways linking GDP, climate, soils, and traits. Results showed that plant functional traits exhibited significant nonlinear responses to GDP, with vegetative structural traits responding more strongly than reproductive traits. The relative contributions of climatic and edaphic drivers differed markedly among traits, with soil fertility and hydroclimatic seasonality emerging as key environmental drivers of GDP-associated trait variation. Structural equation modeling further indicated that GDP primarily promotes vegetative growth through indirect pathways involving soil fertility and hydrological processes, whereas reproductive traits remain mainly influenced by temperature conditions and their extremes. Together, these results show how socioeconomic development redistributes climatic and edaphic controls on plant traits, providing a testable framework for socioeconomic–environmental coupling and ecological prediction.