AME 65:15-27 (2011)  -  DOI: https://doi.org/10.3354/ame01531

ABSTRACT: We examined the phylogenetic diversity and abundance of diazotrophs along a transect from the Pearl River plume to oceanic waters in the northern South China Sea by constructing a clone library and using the quantitative polymerase chain reaction (qPCR). All the diazotrophic phylogenetic groups recovered, including heterotrophic proteobacteria, phototrophic cyanobacteria and Cluster III diazotrophs, showed distinct spatio-temporal variation along the transect. At the oceanic sampling stations, γgammaproteobacteria formed the dominant diazotrophic group, with cyanobacterial diazotrophs accounting for only a relatively small proportion; at the station influenced by the Pearl River plume all the diazotrophs were non-cyanobacterial, making this station distinct from the other stations. Multidimensional analysis demonstrated that salinity was the key environmental factor determining the spatio-temporal variations of diazotrophic communities along the transect. Trichodesmium spp. were the most abundant among the cyanobacterial diazotrophs and were potentially the most important nitrogen fixers at all the oceanic stations. The absence of cyanobacterial diazotrophs in winter, and at the station influenced by the plume, could be due to the relatively high nutrient conditions in these waters.

KEY WORDS: Diazotrophs · nifH gene · Phylogenetic diversity · qPCR · South China Sea