Composition and Activity of N2-Fixing Microorganisms in Mangrove Forest Soils

Mangrove forests are considered to be a highly productive ecosystem, but they also generally nitrogen (N)-limited. Thus, soil N2 fixation can important for the stability of both mangrove ecosystem functions and upland N supply. This study evaluates activity composition relevant microorganisms in two coastal forests—the Guandu an upstream estuary Bali downstream estuary—using acetylene reduction method, real-time polymerase chain reaction, next-generation sequencing. The results demonstrated that ambient nitrogenase was higher (13.2–15.6 nmol h−1 g−1 soil) than (0.2–1.4 soil). However, maximum potential gene (nifH gene) copy number were found forests, implying diazotrophic abundance may not necessarily positively correlated. In addition, amended MoO4 (which inhibits sulfate-reducing bacteria N2-fixation) yielded low activity, made up 20–50% relative indicating these might major active diazotrophs this environment.