Nitrogen inputs are more important than denitrifier abundances in controlling denitrification-derived N2O emission from both urban and agricultural soils.

Abstract Cities are increasingly being recognized as important contributors in global warming, for example by increasing atmospheric nitrous oxide (N 2 O). However, urban ecosystems remain poorly understood due to their functional complexity. Further, few studies have documented the microbial processes governing the N 2 O emissions from urban soils. Here, a field study was performed to assess in situ N 2 O emissions in an urban and agricultural soil located in Xiamen, China. The mechanisms underlying the difference in N 2 O emission patterns in both soils were further explored in an incubation experiment. Field investigations showed that N 2 O emission (3.5–19.0 μg N 2 O-N m−2 h−1) from the urban soil was significantly lower than that from the agricultural soil (25.4–18,502.3 μg N 2 O-N m−2 h−1). Incubation experiments showed that the urban soil initially emitted lower denitrification-derived N 2 O because of the lower nirS (encoding nitrite reductases) abundances, whereas overall N 2 O accumulation during the incubation was mainly controlled by the initial nitrate content in soil. Nitrate addition in a short period (5 days) did not change the total bacterial and denitrifier abundances or the soil bacterial community composition, but significantly altered the relative distribution of some key genera capable of denitrification. Although the urban soil exhibited lower N 2 O emission than its agricultural counterpart in this study, the expanding urban green areas should be taken into account when building N 2 O emission reduction targets. Graphical abstract Unlabelled Image Highlights • The urban soil had significantly lower abundances of nirS and nosZ. • Nitrate shifted neither soil bacterial composition nor denitrifier abundances. • Nitrate changed relative abundances of some genera capable of denitrification. • Nitrate controlled final denitrification-derived soil N 2 O emission. • The urban soil emitted lower N 2 O than the agricultural soil. [ABSTRACT FROM AUTHOR]