Aridity mediates the above‐ and below‐ground biodiversity–ecosystem stability relationship

Understanding the macroecological drivers of biodiversity and ecosystem stability, i.e. the ability of an ecosystem to maintain its structure and function, is crucial to inform how ecosystems can be managed and conserved effectively. Here, we conducted a field survey of plant and soil biota (bacteria, fungi, and nematodes) and estimated the temporal stability of aboveground productivity (ecosystem stability, proxied by normalized difference vegetation index [NDVI]) in 378 plots along an aridity gradient at a 1200 × 1200 km area in the Qinghai‐Tibetan Plateau. We found that ecosystem stability first increased then decreased with thresholds at aridity 0.24 along the spatial gradient. Plant diversity was positively related to ecosystem stability across the aridity gradient, whereas soil biodiversity, particularly fungi, was positively associated with ecosystem stability only under more water‐limited conditions (aridity > 0.2). Mechanisms for maintaining ecosystem stability shifted from plant community to soil fungal community with thresholds at aridity 0.2 along the aridity gradient. Our results underscore that plant and soil biota should be particularly maintained for ecosystem stability under less and more water‐limited conditions, respectively.