Effect of East Asian aerosol enrichment on microbial community composition in the South China Sea

East Asian aerosol has been regarded as an increasingly important nutrient source in the Northwest Pacific region due to intensifying human activities in the last decades. However, its effects on bacterial communities, an important component of the marine microbial food web and biogeochemical cycles, have been little studied. In our study, two types of aerosol enrichment microcosm experiments were conducted in the oligotrophic South China Sea by adding the aerosol initially or daily. Our results showed that the potential stimulus of bacteria by aerosol enrichment was likely masked by a more intense grazing pressure in these treatments. Distinct responses of various bacterial phylogenetic groups, including Actinobacteria, Cyanobacteria, Alphaproteobacteria and Gammaproteobacteria, were revealed by denaturing gradient gel electrophoresis analysis. High aerosol addition resulted in a decrease in autotrophic picocyanobacteria abundance, but no significant composition change was observed. Such responses of microbial abundance and composition could be directly triggered by the input of aerosol-derived organic or inorganic components and further shaped by the changes in the phytoplankton community structure or differentiated mortality loss caused by enhanced protist grazing, which may have implications for oceanic carbon dynamics under future scenarios of increasing atmospheric deposition