Aridity-driven shifts in plant–microbial diversity relationships across the arid and semi-arid grasslands of northern China

Abstract Climate change-driven aridification threatens above- and belowground biodiversity, yet how the relationships between plant diversity and soil microbial diversity change along aridity gradients remains unclear. Here, we conducted a 4,000-km field survey across arid and semi-arid grasslands in northern China. We show that soil conditions, plant diversity, and microbial diversity exhibit sequential threshold responses along the aridity gradient. Beyond these thresholds, plant, bacterial, and fungal diversity generally decline, whereas archaeal species diversity increases. As aridity increases, the negative effects of soil salinity on plant, bacterial, and fungal diversity become stronger, whereas soil salinity shows increasingly positive associations with archaeal species diversity. Plant–bacteria and plant–fungi diversity relationships strengthen in drier regions, whereas plant–archaea relationships become decoupled. These findings show that aridity acts as a strong environmental filter, selecting stress-tolerant species and restructuring plant–microbial diversity coupling in a taxon-specific manner, and highlight the importance of aridity-dependent biodiversity coupling for shaping ecosystem resilience in arid and semi-arid grasslands under ongoing aridification.