Responses of soil N<sub>2</sub>O emissions and their abiotic and biotic drivers to altered rainfall regimes and co‐occurring wet N deposition in a semi‐arid grassland
Yujie Shi, Junfeng Wang, Yunna Ao, Jiayu Han, Zhihan Guo, Xin‐Yuan Liu, Jinwei Zhang, Chunsheng Mu, Xavier Le Roux
Abstract
Abstract Global change factors such as changed rainfall regimes and nitrogen (N) deposition contribute to increases in the emission of the greenhouse gas nitrous oxide (N 2 O) from the soil. In previous research, N deposition has often been simulated by using a single or a series of N addition events over the course of a year, but wet N deposition actually co‐occurs with rainfall. How soil N 2 O emissions respond to altered rainfall amount and frequency, wet N deposition, and their interactions is still not fully understood. We designed a three‐factor, fully factorial experiment with factors of rainfall amounts (ambient, −30%) rainfall frequency (ambient, ±50%) and wet N deposition (with/without) co‐occurring with rainfall in semi‐arid grassland mesocosms, and measured N 2 O emissions and their possible biotic and abiotic drivers. Across all treatments, reduced rainfall amount and N deposition increased soil N 2 O emissions by 35% and 28%, respectively. A significant interactive effect was observed between rainfall amount and N deposition, and to a lesser extent between rainfall frequency and N deposition. Without N deposition, reduced rainfall amount and altered rainfall frequency indirectly affected soil N 2 O emissions by changing the abundance of nirK and soil net N mineralization, and the changes in nirK abundance were indirectly driven by soil N availability rather than directly by soil moisture. With N deposition, both the abundance of nirK and the level of soil water‐filled pore space contributed to changes in N 2 O emissions in response to altered rainfall regimes, and the changes in the abundance of nirK were indirectly driven by plant N uptake and nitrifier (ammonia‐oxidizing bacteria) abundance. Our results imply that unlike wetter grassland ecosystems, reduced precipitation may increase N 2 O emissions, and N deposition may only slightly increase N 2 O emissions in arid and semi‐arid N‐limited ecosystems that are dominated by grasses with high soil N uptake capacity.