Aridity reshapes leaf and root trait dispersion through distinct microbial pathways

Aridity is a primary driver of plant community assembly, yet most trait-based studies focus on mean traits rather than trait dispersion. Soil microbes may mediate plant responses to aridity, but whether leaf and root trait dispersion responds to aridity through shared or distinct microbial pathways remains unclear. Using 535 species-by-plot records (247 species) along an aridity gradient in north-west China, we quantified four leaf and four root traits, soil properties, microbial diversity and composition, and microbial carbon use efficiency. We tested whether aridity differentially regulates leaf vs root functional dispersion (FD_is), and whether these responses are associated with different microbial predictors. Leaf traits shifted more consistently with aridity and were more tightly linked to environmental variation than root traits. Leaf FD_is negatively correlated with CUE, whereas root FD_is negatively correlated with fungal diversity and bacterial community composition. These associations weakened toward less arid sites. Structural equation modeling further showed that leaf FD_is linked primarily to microbial functioning, whereas root FD_is linked more strongly to microbial diversity and composition. Our results reveal that aridity reshapes trait dispersion through organ-specific plant-microbe pathways, highlighting that predicting dryland community responses to increasing drought must treat above- and belowground traits separately.