Abstract
Atmospheric nitrogen (N) deposition usually alters the ratio of resources to stress in terrestrial ecosystems and has important impacts on soil microbiomes. To elucidate the adaptability of soil microbiomes under N deposition scenarios, we conducted a 6-year N addition experiment in a temperate grassland in Inner Mongolia, applying different levels of ammonium nitrate (AN) and urea (AU) to form different resource-to-stress ratio. Our results reveal that the inborn high yield (Y)-resource acquisition (A)-stress tolerance (S) life history strategies of soil microbiomes collectively drive their adaptability to resources and stress under N deposition. Enriched taxa under AN treatment mainly belonged to Actinomycetota and Chloroflexota with Y and S strategies, while those under AU mainly belonged to Pseudomonadota with A and S strategies. Functional preference analysis indicated that bacterial phyla maintained consistent Y-A-S life history strategies across AN and AU treatments. Moreover, strong purifying selection restricted the pace of adaptive evolution, and horizontal gene transfer expanded the functional repertoire in a complementary rather than essential manner. Thus, the adaptation of microbiomes to shifting resources and stress under N deposition scenarios is mainly accomplished by niche conservatism ("move") rather than niche evolution ("evolve"). Our results support the point that it may be easier for microbial species to move into a befitting niche than to evolve to acclimate a new environment.