Responses of soil ammonia-oxidizing bacteria and archaea to short-term warming and nitrogen input in a semi-arid grassland on the Loess Plateau

Ammonia-oxidizing archaea (AOA) and bacteria (AOB) predominantly control ammonia oxidation, the first and rate-limiting step of nitrification, and critically affect plant utilization and the fate of reactive nitrogen (N) input to soil. Both AOA and AOB are often sensitive to environmental changes, but their responses to the concurrent climate warming and N input remain poorly understood, particularly in semi-arid grassland ecosystems where nitrification dominates soil N transformations. We examined the interactive effects of short-term (2-yr) warming and N input (12 g N m(-2) y(-1)) on the abundance and community structure of AOA and AOB in a semi-arid grassland on China's Loess Plateau. Results showed that AOA abundance was significantly higher than AOB in all treatments. N input significantly increased the abundance of AOA and AOB by 32% and 521%, respectively, and induced a significant shift in the AOB community composition. Warming significantly increased the abundance of AOB by 94%, but had no impact on the AOA abundance. Warming (alone or combined with N input) did not significantly affect the community structure of AOA or AOB. These results indicated that AOB was more sensitive to N input and climate warming than AOA in semi-arid Loess grasslands. Our findings suggest that understanding the responses of AOB abundance and composition may be key to predict the N dynamics under future global change scenarios.