Relationships between ammonia-oxidizing communities, soil methane uptake and nitrous oxide fluxes in a subtropical plantation soil with nitrogen enrichment

• Nitrogen addition inhibited CH4 uptake and promoted N2O emission from the subtropical plantation soils.
• The effects of NH4+NH4+ and −NO3NO3− fertilization on soil AOA and AOB abundances and community structure were contrasting.
• Close relationships between ammonia-oxidizers and soil CH4 and N2O fluxes were existed.

Ammonia-oxidizers play an essential role in nitrogen (N) transformation and nitrous oxide (N2O) emission in forest soils. It remains unclear if ammonia-oxidizers affect interaction between methane (CH4) uptake and N2O emission. Our specific goal was to test the impacts of changes in ammonia-oxidizing communities elicited by N enrichment on soil CH4 uptake and N2O emission. Based on a field experiment, two-forms (NH4Cl and NaNO3) and two levels (40 and 120 kg N ha−1 yr−1) of N were applied in the subtropical plantation forest of southern China. Soil CH4 and N2O fluxes, the abundance and structure of ammonia-oxidizing archaea (AOA) and ammonia-oxidizing bacteria (AOB) communities were measured using static chamber-gas chromatography, quantitative PCR (qPCR), and terminal-restriction fragment length polymorphism (T-RFLP). Nitrogen addition tended to inhibit soil CH4 uptake, but significantly promoted soil N2O emission; moreover, these impacts were more significant with NH4+−NNH4+−N than with −NO3−NNO3−−N addition. NH4Cl addition significantly changed ammonia-oxidizer abundance with an increase in AOA and a decrease in AOB. Nitrogen additions significantly decreased the relative abundance of 329 bp and 421 bp of archaeal amoA gene. Negative relationships occurred between soil CH4 uptake and AOA abundance and between soil CH4 uptake and AOA/AOB ratio; however, a positive relationship was found between soil N2O emission and AOA abundance. These results indicate that a shift in abundance and composition of ammonia-oxidizing communities is closely linked to changes in soil CH4 uptake and N2O emission under N enrichment. Furthermore, AOA communities play a contrasting role from AOB communities for regulating the fluctuation between soil CH4 and N2O fluxes.