Soil microbial nitrogen cycle of a drained peatland forest reveals increasing ROLe of nitrification in N2O emissions

Drained peatland forests can be a significant source of nitrous oxide (N2O), a potent greenhouse gas and depleter of stratospheric ozone layer. Restoration of these ecosystems is complicated due to the greenhouse gas emissions associated with rewetting. We aimed to analyse the relationship between the soil microbiome characteristics and emissions of N2O in a drained peatland forest to estimate the effectiveness of peatlands' current and future management practices.

Soil samples from 12 sites within a drained peatland forest in south-eastern Estonia were collected once a month from November 2020 until October 2021 and analyzed for their physical and chemical properties and the abundance of genes associated with nitrogen (N) cycling. qPCR was used to evaluate abundances of specific 16S rRNA genes and following N cycling genes: denitrification (nirS, nirK, nosZ clade I, and nosZ clade II), nitrification (bacterial, archaeal, and COMAMMOX amoA), DNRA (nrfA), and nitrogen fixation (nifH). N2O fluxes were measured by the laser analyser and automated gas chambers throughout the study period.

The water table and soil water content were most significant factors in the emissions of N2O and the abundance of N cycling genes. Bacterial and archaeal 16S rRNA and nirK, nirS, archaeal amoA, and COMAMMOX amoA, were all found to correlate with N2O emissions. Archaeal 16S rRNA and archaeal amoA both positively correlated with N2O. It reveals increasing role of nitrification in the formation of N2O emissions. The other significant genes correlated negatively with N2O emissions but were all strongly linked with water table depth. The N2O flux pattern was characterised by both hot spots with significantly higher N2O emissions, and hot moments with periodically greater N2O emissions. Flooding is most likely the best management practice to decrease N2O emissions in this drained forest.