Program

Ammonia oxidation is the rate-limiting step of the oceanic nitrification, and mainly carried out by ammonia oxidizing archaea (AOA), which plays an important role in the oceanic biogeochemical N-cycle. With AOA amoA gene as the molecular marker, this study applied 454 pyrosequencing to investigate the community structures and activities of free-living and particle-attached AOA in the Pearl River Estuary during summer and winter. Quantitative polymerase chain reaction (qPCR) was used to quantify the AOA amoA gene copy numbers at both DNA and cDNA levels. In summer, the station of mainly freshwater source (A2B) had the highest AOA community diversity but the lowest amoA gene abundances; and the abundance of free-living AOA was 10~1000 times higher than those attached ones. In winter, the station of mainly freshwater source (HM01S and ZJ00S) had the relatively higher community diversity; AOA amoA gene abundance at the DNA level was generally 1000 times higher than those at the cDNA level. Statistical analysis indicated that Salinity was the main environmental factor affecting the community structures of AOA in both seasons, and pH also affecting the AOA community in winter. As for AOA abundance, no significant effects of environmental factors were found at both DNA and cDNA levels. This study demonstrated a clear seasonal shift of the AOA community and abundance in the Pearl River Estuary with salinity as the most influential environmental parameter.