Joint control by soil moisture, functional genes and substrates on response of N2O flux to climate extremes in a semiarid grassland

Abstract

Nitrous oxide (N2O), the third most important greenhouse gas, contributes to the increasing frequency and severity of climate extremes. Disentangling feedbacks of climate extremes on terrestrial N2O emission is important for forecasting future climate changes. Here, we experimentally imposed extreme drought and heat wave events during three years in a semiarid grassland to investigate the responses of N2O flux. We identified that N2O flux suppression during droughts was mediated by soil water content (SWC), microbial biomass carbon (MBC), soil inorganic nitrogen (SIN) and dissolved organic carbon (DOC) contents, and the abundance of archaeal amoA, nirK, and narG. However, bacterial amoA, nirS, and nosZ remained stable. Upon rewetting following droughts, the SWC, SIN, DOC, archaeal amoA, nirK, narG, and resultant N2O fluxes recovered to the magnitude of the ambient control. In contrast, heat waves alone or in combination with drought did not impact N2O fluxes or the underlying physical, chemical and microbial states. Stepwise multiple linear regression suggested that SWC, DOC, and MBC were the key factors regulating immediate responses of N2O flux to climate extremes while the major factors regulating seasonal mean N2O flux in response to climate extremes were archaeal amoA abundance, nirK abundance, and MBC. Our results suggest that N2O fluxes were sensitive to droughts but insensitive to heat waves. Soil moisture induced changes in substrate availability, and the community size of total and functional microorganisms in soil jointly regulated N2O responses to climate extremes. The relative importance of regulating factors shifted at different timescales.