Seasonal Variations in N2O Emissions in a Subtropical Forest With Exogenous Nitrogen Enrichment are Predominately Influenced by the Abundances of Soil Nitrifiers and Denitrifiers

Elevated nitrogen (N) deposition has induced substantial impacts on the emissions of nitrous oxide (N2O) from forest ecosystems, but how soil microbes regulate the production/consumption of N2O under elevated N deposition remains poorly understood, particularly in high N deposition subtropical forests that are characterized by distinct wet-dry seasonality. We established a field N addition experiment in a subtropical forest in southern China to explore the influences of low, medium and high (35, 70, and 105 kg N ha(-1) yr(-1), respectively) N addition on N2O efflux and its associated microbial functional genes [amoA for nitrifiers (ammonia-oxidizing bacteria (AOB) and ammonia-oxidizing archaea (AOA)) and nirK and nosZ for denitrifiers]. The results showed the following: (1) The N2O emissions were stimulated by N addition in the dry season but were depressed in the wet season. (2) The nirK and nosZ abundances were generally stimulated by N addition, whereas the AOB-amoA and AOA-amoA abundances showed divergent responses to N addition. (3) Based on the results of principal component and Pearson correlation analyses, N2O effluxes were associated with microbial biomass in the wet season but with nirK and nosZ abundances in the dry season. Structural equation modeling analyses further indicated that both nitrifiers and denitrifiers under N addition contributed to the generation of N2O in the dry season, whereas the decreased production of N2O in the wet season was primarily caused by denitrifiers. Therefore, seasonally specific strategies should be developed to mitigate the emissions of N2O from subtropical forests with distinct seasonal precipitation patterns.