NirS-type N2O-producers and nosZ II-type N2O-reducers determine the N2O emission potential in farmland rhizosphere soils

Abstract

Denitrification process in agricultural fields is a large source of nitrous oxide (N2O) emitted to the atmosphere. The rhizosphere soils tend to be the hotspots of denitrification in agricultural soils. Recent studies have reported the important role of nosZ II in eliminating N2O. However, little was known about how these more recently discovered N2O-reducing microorganisms together with other N2O-producers affected the N2O emission in agricultural rhizosphere soils. Here, we compared the potential N2O production rate, the denitrification end-product ratio, and the denitrifier communities between rhizosphere and non-rhizosphere soils of two types of crops in winter and summer. The potential activities were measured by acetylene inhibition technique. QPCR analysis was used to quantify the functional genes. High-throughput sequencing and clone library were conducted to analyze the community structure of denitrifiers. The rhizosphere soils had a higher N2O production potential but lower denitrification end-product ratio (N2O/(N2O+N2)) than the non-rhizosphere soils. The potential N2O production rate was correlated to the nirS-bacteria abundance, especially in terms of the genus Azospirillum. The N2O/(N2O+N2) ratio showed a negative correlation with both the diversity and abundance of the nosZ II-type N2O-reducers. Altogether, we propose that nirS-type N2O-producers and nosZ II-type N2O-reducers can affect the N2O emission in agricultural rhizosphere soils, and enhancement of diversity and abundance of nosZ II-type N2O-reducers may help with the N2O mitigation from upland crops.