Impact of Management on Tropical Peatland Nitrogen Cycle: Soil Microbiome and N2O and N2 Fluxes

Nitrogen is a naturally occurring element vital for all organisms; thus, its management is economically, ecologically and environmentally critical. Microbes mediating biogeochemical processes control the quantity and distribution of nitrogen; however, the lack of knowledge regarding microbial processes governing N2O and N2 emissions hinders climate-change impact estimations of tropical peatlands. This study aimed to discover the key players of soil microbial communities controlling gaseous fluxes (N2O and N2) under different land uses in tropical peatlands.

The peat sampling from topsoil was carried out at natural and managed tropical peatland sites in America (Florida, Pantanal, Peru, and French Guiana), Africa (Uganda), and Asia (Borneo, Myanmar, Taiwan). Metagenomics, metabarcoding and quantitative PCR were used to characterize soil microbiome, and potential N2 emissions and in situ N2O emissions and physicochemical parameters were measured.

Based on the balanced weighted phylogenetic diversity index, we found that denitrification (nirK and nosZ) and N-fixation (nifH) gene phylogenetic diversities were significantly smaller in managed sites compared to natural ones. The reduction in denitrifiers' and nitrifiers' phylogenetic diversity increased gaseous emissions in both studied land uses: 1) composition of archaeal amoA-type nitrifiers was negatively correlated with N2O emissions in managed sites; 2) composition of nirK- and nosZ-type denitrifiers were negatively associated with N2O emission in natural sites. Conversion of N2O to N2 was mainly controlled by microbes possessing nosZI genes in the wet sites and microbes possessing nosZII genes in the managed sites. Denitrification taxa are relatively diverse in both sites. amoA-harbouring archaea from genus Nitrosoarchaeum were dominant at the natural sites and from genus Nitrososphaera at the managed sites. nrfA gene-possessing microbes (DNRA, dissimilatory nitrate reduction to ammonium) influenced the N2O emissions. DNRA process is governed in managed sites by Anaeromyxobacter and Myxococcus but in natural sites by Carboxydothermus and Slackia.