Seasonal variation of anaerobic ammonium oxidizing bacterial community and abundance in tropical mangrove wetland sediments with depth

Anaerobic ammonium oxidation (anammox) process was found to make a nonnegligible contribution to nitrogen loss in estuarine and coastal ecosystems in recent years. In order to better understand ecological characteristics of anammox bacteria in coastal ecosystems, 16S rRNA gene clone library and real-time quantitative PCR (qPCR) were used to investigate the diversity and abundance of anammox bacteria in sediments of the Dongzhai Harbor mangrove wetland in Hainan, China. Sediments at different depths along a transect from mangrove trees to mudflats were studied in March (spring) and August (summer). The dominant genera of anammox bacteria observed in both seasons were Kuenenia spp. and Scalindua spp. The diversity and abundance of anammox bacteria showed not only seasonal variations, but also differences with depths and habitats. Anammox bacteria appeared to be more abundant and had higher diversity in August than in March. In addition, lower layer (40-45 cm) sediments and mangrove sediments had higher abundance and diversity of anammox bacteria than surface layers (0-2 cm) and non-mangrove areas. It was suggested that water pH, salinity and sediment nitrite, nitrate and ammonium might be key factors shaping the community structure and distribution of anammox bacteria. This study further indicated that the mangrove ecosystem might provide a favorable niche for anammox bacteria and thus plays an important role in nitrogen cycling. Overall, these results extend our current knowledge about the structure and dynamics of anammox bacterial community in the mangrove ecosystem.