Aridity-related differences in soil elemental ratios reshape microbial functional traits across global biomes.

Aridity alters soil carbon (C), nitrogen (N) and phosphorus (P) stoichiometry, yet the implications of these processes for soil microbial functional traits and potentials at the genomic level remain poorly synthesized. Here we combine measurements of soil C, N and P pools and ratios with shotgun metagenomes from 200 natural ecosystems spanning major biomes worldwide. Across sites, increased aridity is associated with lower soil C:N and N:P (and C:P) ratios and with a coordinated shift in microbial functional potential. Genes linked to catabolic resource acquisition-including carbohydrate-active enzymes and pathways for degradation of plant litter and organophosphorus compounds-are declined as C becomes relatively scarce. In contrast, genes supporting anabolic investment in growth and drought resistance, such as RNA transcription, protein synthesis and intracellular transport, are increased. These patterns indicate that aridity-related change in soil elemental ratios is coupled to a broad shift from catabolic to anabolic strategies in soil microbiomes. By linking soil elemental ratios to microbial functional traits across biomes, our study provides a framework for anticipating how climate-driven drying may reorganize microbial metabolism with consequences for carbon and nutrient cycling.