Hot spots and hot moments of N2O fluxes explained by monthly dynamics of soil microbiome in drained peatland forest

The nitrogen (N) cycle involves intricate interactions affected by the spatial and temporal variability. Hot moments, occurring short-lived across seasons, significantly contribute to temporal nitrous (N₂O) emission fluctuations. Likewise, N₂O emissions exhibit localized spatial variability as hot spots. Year long monthly based studies of soil N cycle microbiome dynamics in peatland forests are unknown. This study investigates the relationship between soil microbial communities and N₂O gaseous fluxes within a drained peatland forest throughout a year. Key research questions are: how are the genes responsible for N cycling in the peatland spatially and temporally distributed?; what patterns are there between soil characteristics (e.g., soil water content, soil temperature and pH) and N cycling gene abundances?

Soil samples from 12 sites within a drained peatland forest in south-eastern Estonia were collected over a year and analysed for their physical and chemical properties and the abundance of genes associated with N cycling. Quantitative polymerase chain reaction was used to evaluate the bacterial and archaeal community abundances by quantifying the abundances of specific 16S rRNA genes and to evaluating the abundances of 10 genes associated with N cycling: denitrification (nirS, nirK, nosZ clade I, nosZ clade II, and fungal nirK), nitrification (bacterial, archaeal, and comammox amoA), DNRA (nrfA), and N fixation (nifH). This data was paired with N₂O flux data collected in automatic dynamic gas chambers throughout the study period.

Spatial variations apparent in the soil's chemical and physical composition reveal distinct vegetation and microbial communities across the area. Archaeal 16S rRNA, along with genes associated with N cycling (fungal nirK, nosZI, bacterial and comammox amoA), exhibited correlations with N₂O emissions. Archaeal 16S rRNA, bacterial amoA, fungal nirK, and nosZI were positively correlated with N₂O emissions. Throughout the year, water table levels and volumetric water content significantly influenced both N₂O emissions and the abundance of N cycling genes. The site encompasses specific areas with consistently higher N₂O emissions (hot spots) and periodic peaks in emissions (hot moments) due to the combined interplay of physical, chemical, and genetic attributes within the peatland soil.