Diversity-multifunctionality relationships shift with increasing aridity in grasslands

Grasslands are a dominant global ecosystem, yet they face an uncertain future due to the accelerating threat of aridification, particularly in drylands. Species diversity and functional diversity can enhance the resilience of grasslands to aridity and help to maintain multiple ecosystem functions (multifunctionality) to face these challenges. Yet, the relative roles of species diversity and functional diversity in promoting this resilience are not well understood. We examined how diversity-multifunctionality relationships varied with increasing aridity, and explored the underlying mechanisms at 104 grassland sites spanning an extensive aridity gradient in China. Our results indicate that positive diversity-ecosystem multifunctionality relationships strengthened with increasing aridity but waned at aridity levels exceeding 0.83, a region that corresponds to the transition between semiarid and arid climates. This threshold also coincided with a shift in the relative importance of functional diversity and species diversity. Specifically, functional diversity was more strongly associated with multifunctionality under wetter conditions, but under drier conditions, species diversity, particularly plant diversity, played a more dominant role. Predicted drier conditions would promote a more diverse grassland community, but not necessarily species with more diverse traits. Our results suggest that enhancing species diversity can mitigate the impacts of intensified aridification in grasslands under a drier climate. These finding demonstrate the importance of protecting species-rich grasslands as the planet becomes hotter and drier. By prioritizing climate-specific biodiversity management and matching actions to particular dimensions of diversity, grassland managers can ensure that diversity benefits translate into tangible gains in ecosystem services and climate resilience.