1. Biodiversity can stabilise productivity through different mechanisms, such as asynchronous species responses to environmental variability and species stability. Global changes, like intensified drought, could negatively affect species richness, species asynchrony, and species stability, but it is unclear how changes in these mechanisms will affect stability of aboveground primary productivity (ANPP) across ecosystems.

2. We studied the effects of a 4-year extreme drought on ANPP stability and the underlying mechanisms (species richness, species asynchrony, and species stability) across six grasslands in Northern China. We also assessed the relative importance of these mechanisms in determining ANPP stability under extreme drought.

3. We found that extreme drought decreased ANPP stability, species richness, species asynchrony, and species stability across the six grasslands. However, structural equation modelling revealed that species asynchrony, not species richness or species stability, was the most important mechanism promoting stability of ANPP, regardless of drought across the six grasslands.

4. Synthesis: Our results suggest that species asynchrony, not species richness and species stability, consistently buffers ecosystem stability against extreme drought across and within grasslands spanning a broad precipitation gradient. Thus, species asynchrony may be a more general mechanism for promoting stability of ANPP in grasslands in the face of intensified drought.