Microbiome dynamics associated with soil nitrous oxide pulses driven by N fertilization and dry-rewet events

Increasing frequency of dry-rewet events could result in a flush of soil nutrient turnover, but how active soil microbiomes and N2O production respond to the “Birch effect” remains uncertain. Here, a laboratory mesocosm experiment was conducted to assess active microbial diversity and composition associated with N2O pulses affected by N fertilization and dry-rewet treatments. Real-time monitoring of greenhouse gas production showed that dry-rewet events stimulated N2O emissions even in unfertilized mesocosms. Both DNA- and RNA-based amplicon sequencing of 16S and ITS rRNA markers showed that dry-rewet treatments affected active microbiomes in soil RNA pools more significantly than DNA, and that bacterial/archaeal communities were more sensitive to dry-rewet stressors than fungi. Both microbial Chao1 richness and Shannon diversity were suppressed by dry-rewet treatments. Dry-rewet events stimulated Actinobacteria and Firmicutes, but repressed other bacterial groups in both two depths of soil RNA and DNA. In top layer of active fungal community, dry-rewet treatments enhanced Ascomycota, but reduced Basidiomycota, Glomeromycota, and Zygomycota. Dry-rewet stressors also increased the complexity and altered the patterns of co-occurrence networks of both bacterial/archaeal and fungal communities. Some active bacterial denitrifiers, such as Bacillus and Pseudomonas, were found to be closely associated with changes induced by dry-rewet events and potentially responsible for the observed large and rapid N2O pulses under mesocosm conditions.