Threshold-dependent shifts in ecosystem stability across aridity gradients on the Mongolian Plateau

Global aridification threatens dryland ecosystems biodiversity and stability, yet the influence of multidimensional biodiversity on stability across aridity gradients is complex and context-dependent. Here we analyze plant and soil microbial diversity (taxonomic, phylogenetic, functional) across a 3,000-kilometer aridity gradient on the Mongolian Plateau and use multi-year observations from two validation sites. We identify a critical aridity threshold (Aridity ≈ 0.83) where stability mechanisms abruptly shift. Below this threshold (less arid conditions), ecosystem stability is positively linked to plant and fungal taxonomic richness. Above it (more arid conditions), stability correlates with conservative plant traits (lower special leaf area) and lower phylogenetic diversity, reflecting environmental filtering for stress-tolerant species. This transition is driven by a shift from C3 to C4 plant dominance, altering community traits and plant-microbial interactions. While our correlational findings require experimental confirmation, they challenge linear stability models, highlighting the importance of threshold-dependent biodiversity-environment interactions for dryland management. Ecosystem stability shifts at an aridity threshold where in less arid conditions it is linked to plant and fungal richness and in more arid conditions it depends on conservative plant traits and lower phylogenetic diversity, based on sampling across a 3000-km Mongolian Plateau gradient.