Plant diversity within communities, not among them, stabilizes grassland productivity across spatial scales.

Evidence shows that local functional trait composition and diversity along the fast-slow leaf economics spectrum can predict the temporal stability of community productivity in response to environmental changes. However, it remains unclear whether these relationships persist at larger spatial scales. Combining a field survey of plant diversity with remote sensing estimates of primary productivity across a large environmental gradient in 235 grasslands across the Qinghai-Tibet Plateau and the Inner Mongolia Plateau, we find that species richness contributes to stabilizing productivity, while functional diversity contributes to destabilizing productivity at the local scale. In contrast, we find no evidence that variation in species richness and functional diversity among local communities contributes to stabilizing productivity across larger spatial scales. While the relationships between environmental conditions and local diversity and stability differ between the two regions, the overall positive relationships between diversity and stability are consistent at both the local and larger spatial scales. Our study offers insights into how functional traits along the fast-slow leaf economics spectrum mediate the effects of environmental factors (e.g., precipitation) on ecosystem stability at contrasting spatial scales.