The Impacts Of Adding Inorganic Nutrients On Dissolved Organic Carbon Utilization By Marine Heterotrophic Bacteria

Marine heterotrophic bacteria are important component of the picoplankton, play an important role in marine ecosystems, and shoulder the burden of biology elements recirculation. The relationship between organic matter and heterotrophic bacteria has been the key point of marine heterotrophic bacteria biogeochemistry cycles and ecology. As the major component of Microbial loop and Microbial Carbon Pump, marine bacteria participate in the main process of the dissolved organic carbon (DOC) metabolism. Increasing availability of inorganic nutrients has been confirmed to stimulate the growth of phytoplankton in the former studys, however, little is known about the impact of inorganic nutrients to bacteria growth and carbon uptake. Based on the MCP framework, we conducted the experiments to study the effects of inorganic nutrients on the bacterial uptake DOC through incubations with one pure culture bacteria strain and with in situ communities under different nutrients conditions using biological and chemical parameters. Results are showed as follows:For the pure culture experiment, we used one pure culture strain JL354(one model strain of the aerobic anoxygenic phototrophic bacteria, AAPB JL354) as an example. Experiments were carried out using glucose as the one only carbon source under different nutrients condition. The results showed that:Firstly, under one carbon source condition, increasing inorganic nutrients can stimulate the bacterial uptake of the glucose. Secondly, the production of fluorescence dissolved organic matter (FDOM) in the JL354incubation existed differences at different nutrient gradient. There was no change of protein like fluorescence matter in the different nutrient conditions. Humic like fluorescence matter with high molecular weight and aromaticity increased along with increasing nutrients, while humic like fluorescence matter with low molecular weight and aromaticity decreased simultaneously. Thirdly, nutrients could decrease the concentration of particle organic carbon (POC) of JL354and increase the concentration of particle organic nitrogen (PON), which was disadvantageous for POC storage. Finally, the DOC concentration of the final culture medium with JL354decreased with nutrient enrichment. These results showed that increasing inorganic nutrients could stimulate the bacterial uptake of DOC and released more CO2back to atmosphere.We conducted the in situ studies in the East China Sea with nutrient gradient conditions. Incubations with the enrichment of inorganic nutrients were carried out at five stations. The results showed that:firstly, nutrients enrichment had different impacts on bacteria at the different environments. Secondly, inorganic nutrients could directly excite bacteria in the barren areas of the ECS, while no such change occured in the eutrophic area. Thirdly, inorganic nutrients could stimulate bacterial growth and the bacterial consumption of the TOC directly, and the DOC might mainly be semi-labile DOC. And the semi-labile DOC might contain FDOM such as T peak-protein like. Finally, molecular results showed that some bacterial community with nasA could be influenced by the nutrients enrichment, which could have the ability of utilizing the "one single carbon compound".Marine bacteria were thought as the one of the major components of MCP. Both pure bacterial culture in the lab and the incubations in the barren area of the ECS showed that more nutrients addition could bring more bacterial carbon consumption, stimulated marine bacterial growth. Our results indicated that the MCP process could be affected by the inorganic nutrients directly.