Tree plantations influence the abundance of ammonia-oxidizing bacteria in the soils of a coral island

The roles of ammonia-oxidizing archaea (AOA) and ammonia-oxidizing bacteria (AOB) in soil nitrogen cycling are well understood, but the importance of these bacteria is often overlooked when establishing tree plantations. Seedings of three tree species (Cocos nucifera (CN), Calophyllum inophyllum (CI), and Cerbera manghas (CM)) were transplanted from a mainland (ML) plantation nursery to a tropical coral island in Hainan province, China, for restoration purposes. Here, we investigate the impacts of these tree plantations on AOA and AOB abundances. We compared the AOA and AOB abundances in soils from the island after tree plantation establishment, from barren land (BL) on the island and from the ML by quantifying amoA gene copies. Compared with BL, tree plantations significantly increased the abundance of AOB but had little influence on the abundance of AOA. Moreover, the AOB abundance in the island soil after the CM plantation establishment was comparable to that in the ML soil. Our results demonstrated that tree plantations can promptly restore AOB but not AOA communities in tropical barren islands, and therefore revealing the crucial role of tree plantation establishment in affecting AOB-induced ammonia oxidation, a rate-limiting step in N cycling.