Abstract:Coastal wetlands are ecosystems between terrestrial and marine ecosystems, which are highly diverse and also result in highly diverse microbial communities. In the last several decades, an increasing nitrogen load into coastal wetland ecosystems causes serious environmental problems such as eutrophication, and harmful algal blooms. Here we review the microbial communities involved in nitrogen cycling processes, such as nitrogen fixation, nitrification, denitrification, anaerobic ammonium oxidation, dissimilatory nitrate reduction to ammonium processes, and their key functional genes including nifH, amoA, hzo, nirK, nirS and nrfA as well as related environmental factors to further understand the microbially-driven nitrogen cycling processes for potentially removing nitrogen to mitigate eutrophication and harmful algal blooms.