Demographic and growth dynamics jointly shape grassland productivity under extreme drought

Understanding how plant communities maintain productivity in arid environments remains a key ecological question. Using two independent 4–year drought experiments with a 66% reduction in growing season precipitations in a semi-arid grassland, we found that reduction in plant density and individual size jointly contribute to drought-induced declines in aboveground net primary productivity (ANPP), and that their relative importance depends on drought duration, intensity, and functional group. For graminoids, ANPP decline was primarily driven by shrunk individual size, whereas for forbs it was driven by reduced plant density. We observed a trade–off between the contributions of plant density and individual size to productivity, which was mediated by leaf functional traits, such as leaf carbon content (LCC) and leaf nitrogen (LNC). Our findings highlight the role of the trade-off between demographic and growth-related processes in regulating productivity under climate change.