Response of soil N2O emissions to precipitation pulses under different nitrogen availabilities in a semiarid temperate steppe of Inner Mongolia, China

Short-term nitrous oxide (N2O) pulse emissions caused by precipitation account for a considerable portion of the annual N2O emissions and are greatly influenced by soil nitrogen (N) dynamics. However, in Chinese semiarid temperate steppes, the response of N2O emissions to the coupling changes of precipitation and soil N availability is not yet fully understood. In this study, we conducted two 7-day field experiments in a semiarid temperate typical steppe of Inner Mongolia, China, to investigate the N2O emission pulses resulting from artificial precipitation events (approximately equivalent to 10.0 mm rainfall) under four N addition levels (0, 5, 10, and 20 g N/(m(2)center dot a)) using the static opaque chamber technique. The results show that the simulated rainfall during the dry period in 2010 caused greater short-term emission bursts than that during the relatively rainy observation period in 2011 (P < 0.05). No significant increase was observed for either the N2O peak effluxes or the weekly cumulative emissions (P > 0.05) with single water addition. The peak values of N2O efflux increased with the increasing N input. Only the treatments with water and medium (WN10) or high N addition (WN(2)0) significantly increased the cumulative N2O emissions (P < 0.01) in both experimental periods. Under drought condition, the variations in soil N2O effluxes were positively correlated with the soil NH4-N concentrations in the three N input treatments (WN5, WN10, and WN(2)0). Besides, the soil moisture and temperature also greatly influenced the N2O pulse emissions, particularly the N2O pulse under the relatively rainy soil condition or in the treatments without N addition (ZN and ZWN). The responses of the plant metabolism to the varying precipitation distribution and the length of drought period prior to rainfall could greatly affect the soil N dynamics and N2O emission pulses in semiarid grasslands.