Microorganisms carrying nosZ I and nosZ II share similar ecological niches in a subtropical coastal wetland.

Nitrous oxide (NO) reducers are the only known sink for NO and pivotal contributors to NO mitigation in terrestrial and water ecosystems. However, the niche preference of nosZ I and nosZ II carrying microorganisms, two divergent clades of NO reducers in coastal wetlands, is not yet well documented. In this study, we investigated the abundance, community structure and co-occurrence network of nosZ I and nosZ II carrying microorganisms and their driving factors at three depths in a subtropical coastal wetland with five plant species and a bare tidal flat. The taxonomic identities differed between nosZ I and nosZ II carrying microorganisms, with nosZ I sequences affiliated with Alphaproteobacteria and Betaproteobacteria while nosZ II sequences with Gemmatimonadetes, Verrucomicrobia, Gammaproteobacteria, and Chloroflexi. The abundances of nosZ I and nosZ II decreased with increasing soil depths, and were positively associated with salinity, total carbon (TC) and total nitrogen (TN). Random forest analysis showed that salinity was the strongest predictor for the abundances of nosZ I and nosZ II. Salinity, TC and TN were the major driving forces for the community structure of nosZ I and nosZ II carrying microorganisms. Moreover, co-occurrence analysis showed that 92.2 % of the links between nosZ I and nosZ II were positive, indicating that nosZ I and nosZ II carrying microorganisms likely shared similar ecological niches. Taken together, we provided new evidence that nosZ I and nosZ II carrying microorganisms shared similar ecological niches in a subtropical estuarine wetland, and identified salinity, TC and TN serving as the most important environmental driving forces. This study advances our understanding of the environmental adaptation and niche preference of nosZ I and nosZ II carrying microorganisms in coastal wetlands.