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Precipitation changes exert a fundamental effect on the nitrogen (N) cycle in water‐limited grasslands. Soil microbes are essential drivers of N cycle, and the rates and their stabilities of interrelated N‐cycling processes are reflected by the abundance and diversity of N‐cycling genes. Yet, little is known about how altered precipitation affects the genes involved in the entire N‐cycling pathways.By combining a 6‐year precipitation manipulation experiment (−30%, ambient, +30%, +50%) with metagenomic sequencing, we investigated the responses of N‐cycling gene abundance and diversity to altered precipitation at two soil depths (0–10 and 30–50 cm).We found that increased precipitation enhanced the abundance of numerous key genes, leading to an acceleration of N turnover, but decreased the diversity of ammonium assimilation genes. Decreased precipitation did not reduce abundance or diversity of N‐cycling genes. Most N‐cycling genes showed generally consistent responses to altered precipitation in the topsoil (0–10 cm) and subsoil (30–50 cm), albeit with clear distinctions in both abundance and diversity by soil depth. These precipitation‐specific responses and depth‐dependent variabilities of functional genes were attributed to the distinct taxonomic composition of each N‐cycling gene. Furthermore, we quantified gross N transformation rates and found that they were well predicted by the abundance of most N‐cycling genes (e.g. genes involved in ammonium assimilation and nitrification).Our study sheds new light on the soil N cycle under precipitation alterations from the perspective of individual gene abundance and diversity and shows that future increases in precipitation could accelerate soil N turnover in arid and semi‐arid lands. Read the free Plain Language Summary for this article on the Journal blog. [ABSTRACT FROM AUTHOR]

Semi-arid ecosystems play an important role in regulating the dynamics of the global terrestrial CO2 sink. These dynamics are mainly driven by increasing inter-annual precipitation variability. However, how ecosystem carbon processes respond to changes in precipitation is not well understood, due to a lack of substantial experimental evidence that combines increased and decreased precipitation treatments., This study, a 3-year field manipulation experiment with five precipitation levels conducted in a semi-arid steppe, examined the impacts of increased and decreased precipitation on ecosystem CO2 ( GEP: gross ecosystem photosynthesis; ER: ecosystem respiration; NEE: net ecosystem CO2 exchange), water exchange ( ET: evapotranspiration), and resource use efficiency ( CUE: carbon use efficiency; WUE: water use efficiency)., We found that decreased precipitation reduced ecosystem CO2, water exchange and resource use efficiency significantly, while increased precipitation did not cause significant influence on them. That is, they responded more sensitively to decreased precipitation. Soil water availability was the most important driver determining changes in GEP, ER and ET. Changes in NEE, CUE and WUE were predominately regulated by soil temperature. Photosynthesis at leaf and ecosystem levels showed significantly greater sensitivity to changed precipitation than respiration and ET, and therefore determined the trends of net carbon uptake and resource use efficiency., This study highlighted an asymmetric response of ecosystem carbon and water processes to altered precipitation. This is potentially important for improving our understanding of how possible future changes in precipitation will affect the carbon cycle. Taking this asymmetric response into consideration will inevitably reduce uncertainties in predicting the dynamics of the global carbon cycle., A is available for this article. [ABSTRACT FROM AUTHOR]