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‐1yr‐1, respectively) N addition on N2O efflux and its associated microbial functional genes [amoAfor nitrifiers (ammonia‐oxidizing bacteria (AOB) and ammonia‐oxidizing archaea (AOA)) and nirKand nosZfor 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 nirKand nosZabundances were generally stimulated by N addition, whereas the AOB‐amoAand AOA‐amoAabundances 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 nirKand nosZabundances 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. Tropical and subtropical forests are considerable sources of nitrous oxide (N2O), one of the greenhouse gases mainly produced via microbial nitrification and denitrification in soil. In recent decades, the emissions of N2O have been influenced by increasing nitrogen (N) deposition due to enhanced atmospheric reactive N derived primarily from human activities. Moreover, among the types of N deposition, wet N deposition depends greatly on precipitation. This dependence makes predicting future change trends in N2O emissions challenging, especially in tropical and subtropical forests in southern China due to the large amount of natural N deposition and the distinct wet‐dry seasonality caused by unevenly distributed annual precipitation in this region. We studied the responses of N2O emissions to increasing N deposition by establishing a field N addition experiment in a subtropical forest in southern China. We explored the responsive differences in N2O emissions between wet and dry seasons from microbial regulation aspects. The N addition depressed N2O emissions in the wet season but stimulated N2O emissions in the dry season. Moreover, microbial biomass in the wet season and denitrifier abundance in the dry season were the indicators of N2O emissions in response to elevated N deposition. N2O emissions from the subtropical forest soils were stimulated in the dry season but depressed in the wet season by N additionThe abundances of nitrifying/denitrifying functional genes were more responsive to N addition than to wet‐dry seasonal changesN2O effluxes were associated with microbial biomass in the wet season but with denitrifying gene abundances in the dry season