Aridity modulates the contribution of plant and soil diversity to grassland stability

Growing evidence underscores the critical role of plant and soil diversity in enhancing multiple facets of ecosystem stability, including temporal invariability, resistance, and resilience to climate variability. However, the combined effects of plant and soil diversity on ecosystem stability along environmental gradients remain unclear. Here, we investigated 52 sites along a 1200-km precipitation gradient across the Tibetan Plateau, spanning both mesic (>150 mm mean annual precipitation) and xeric (<150 mm) grasslands. We examined the contribution of plant and soil fungal diversity to ecosystem stability of community productivity. Our results show that plant diversity consistently enhances temporal invariability in both mesic and xeric grasslands. In contrast, soil fungal diversity is negatively related to resistance and resilience in xeric grasslands but shows no such relationship in mesic grasslands. Specifically, in mesic grasslands, arbuscular mycorrhizal fungal diversity promotes resilience, whereas plant pathogen diversity reduces it. In xeric grasslands, resistance and resilience decline with arbuscular mycorrhizal fungi diversity but improve with soil saprobe diversity. These findings emphasize that the role of plant and soil biodiversity in maintaining ecosystem stability depends on aridity levels, underscoring the need for region-specific biodiversity conservation strategies to sustain ecosystem functions under climate change.