Rates and microbial communities of denitrification and anammox across coastal tidal flat lands and inland paddy soils in East China

Denitrification and anammox are the main pathways of N loss in wet habitats while their relative contribution to N2 production and underlying microbial mechanisms across marine-terrestrial ecotone remain unclear. Here we investigated the rates of anammox and denitrification, and the distribution patterns of anammox bacteria and nosZ clade I and II denitrifiers across coastal tidal flat to inland paddy soils. Results showed that denitrification dominated the N2 production over anammox in all samples, accounting for 87.1%-100% of total N2 production. Coincident with the rate, the abundance of nosZ clade I and II genes were 1-2 orders of magnitude higher than those of hzsB gene. The community of anammox bacteria was mainly driven by salinity while nosZ clade I and II denitrifiers communities were mainly determined by both salinity and pH. Alphaproteobacteria dominated in the nosZ clade I community in all samples while Betaproteobacteria and Gammaproteobacteria were mainly present in low salinity wetland and paddy soils. The nosZ clade II community was composed of more phyla, in which Bacteoidetes and Chloroflexi were ubiquitous while Gemmatimonadetes was present only in low salinity wetland and paddy soils. These findings have direct implications for explicitly incorporating both nosZ clade I and II into future N loss estimation and N2O mitigation in marine-terrestrial ecotone.