Hot Moments of N2O Emission Under Water and Nitrogen Management in Three Types of Steppe

Hot moments of soil nitrous oxide (N2O) emission contribute to large fractions of total annual emissions. Magnitudes of N2O emission during hot moments to increasing water and nitrogen (N) availabilities in different steppe types were not well understood. Based on soil monoliths collected from three steppes (meadow, typical, and desert steppes) in northern China, we found that the typical steppe held the lowest N2O emission among the three steppes. Water and N co-addition could increase soil N2O emission by up to 245-fold. Water addition significantly enhanced soil N2O emission in all the three steppes, but the sensitivity of soil N2O emission to water addition decreased from desert steppe (r(2) = 0.83) to typical (r(2) = 0.73) and meadow (r(2) = 0.66) steppes. Nitrogen addition significantly promoted soil N2O emission only in the meadow steppe where soil C:N was relatively higher than the other two steppes. Water and N addition displayed strong positive interaction on soil N2O emission in the meadow steppe while negative interaction in the typical steppe. Different responses of plants, microorganisms and soil NO3- concentration drove the variation in magnitude of soil N2O emission between the two steppes. Our results illustrate different interactions of water and N addition on hot moments of soil N2O emission in the three steppes. We suggest that the pulsed feature of N2O emission should be taken into account in prediction of greenhouse gas emission in the global arid and semiarid grasslands.