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Rainfall patterns are predicted to change dramatically in many terrestrial landscapes, including drylands. The most limiting resources for plant growth in arid regions is nitrogen (N) as well as water. A natural aridity gradient provides appropriate candidate conditions for predicting the impacts of changes in rainfall on soil N dynamics. To comprehensively and mechanistically examine soil N dynamics, we focused on the steps of N transformation, their microbial drivers, and the determining soil properties. We divided the N transformation process into three steps: (i) organic matter degradation, (ii) N mineralization, and (iii) nitrification, which are driven primarily by fungi, prokaryotes, and ammonia oxidizers, respectively. Soil samples were collected from three black locust forests with mean annual precipitations ranging from 449 to 606 mm. Along the aridity gradient, all three steps changed while maintaining a …