Aridity regulates scale-dependent effects of multiple resource additions on productivity stability in Eurasian grasslands

Increasing the supply of multiple limiting resources generally reduces biodiversity and community stability in grasslands. Aridity is known to modify biodiversity-stability relationships, yet it remains unclear whether the effects of multiple resource supply on biodiversity and stability vary along aridity gradients and across spatial scales. Here, we examine how aridity mediates the responses of biodiversity and stability at multiple scales to increasing the number of added resources (e.g., water and nutrients) in Eurasian grasslands. Increasing the number of added resources reduced local plant species richness, asynchronous biomass dynamics among local communities (spatial asynchrony), and the stability of productivity at larger spatial scales, but had no effect on local-scale productivity stability. The negative effects of multiple resource addition on diversity, spatial asynchrony and large-scale productivity stability weakened with increasing aridity, with more arid grasslands showing weaker responses. Mechanistically, increasing resource supply reduced large-scale productivity stability primarily by reducing spatial asynchrony, while increasing aridity weakened the contribution of spatial asynchrony to large-scale productivity stability. Overall, our results demonstrate that the negative effects of multiple resource supply on grassland stability are scale-dependent and strongly regulated by aridity. Increasing inputs of water and nutrients are reshaping grassland ecosystems worldwide, yet their ecological effects may vary across aridity gradients and spatial scales. The study shows that increasing aridity weakens the negative effects of multiple resource additions on large-scale productivity stability by reducing the stabilizing role of spatial asynchrony.