Revealing structure and assembly for rhizophyte-endophyte diazotrophic community in mangrove ecosystem after introduced Sonneratia apetala and Laguncularia racemosa.

Biological nitrogen fixation (BNF) mediated by diazotrophic communities is a major source of bioavailable nitrogen in mangrove wetlands, which plays important roles in maintaining the health and stability of mangrove ecosystems. Recent large-scale mangrove afforestation activities have drawn great attention due to introduced mangrove species and their potential impacts on bio-functionalities of local ecosystems. However, the effects of introduced mangrove species on diazotrophic communities remain unclear. Here, we analyzed rhizosphere and endosphere diazotrophic communities between native mangrove species (Avicennia marina) and introduced mangrove species (Sonneratia apetala and Laguncularia racemose) by sequencing nifH gene amplicons. Our results showed that S. apetala and L. racemose introduction significantly (P < 0.05) increased nutrition components (e.g., total carbon and total nitrogen) in rhizosphere, as well as the diazotrophs richness in rhizosphere and endosphere. The relative abundance of clusters III diazotrophs in the rhizosphere and Rhizobium in the endosphere were significantly increased with L. racemosa or S. apetala introduction. Fe and pH were the main environmental factors driving the divergence of endophyte-rhizophyte diazotrophs between native and introduced mangroves. The correlation-based network analyses indicated that the interaction among rhizophyte-endophyte diazotrophs is more harmonious in native mangrove, while there exist more competition in introduced mangroves. These findings expand our current understanding of BNF in mangrove afforestation, and providing new perspectives to sustainable management of mangrove ecosystem.