Abstract
Biodegradation of dissolved organic carbon (DOC) is the critical process that controls DOC turnover time, as well as horizontal and vertical carbon export in the ocean. However, previous work still showed incompatible results about impacts of environmental factors to DOC accumulation and remineralization, for example, nutrients limitation and microbial community structure. Kuroshio intrusion has a major impact to the energy and material exchange between South China Sea (SCS) and Pacific Ocean, which also provides an ideal environmental gradient to study degradation mechanisms of DOC. Here we show impacts of different microbial community structures and nutrients levels on biodegradable DOC by applying the onboard incubation experiments. Using 16s rRNA analysis, we found significant difference in microbial community structure between Kuroshio and SCS surface waters. Besides, we found that 6.5% (± 0.5%) of Kuroshio DOC (5.2 ± 0.4 μM) was degraded by SCS microorganisms, higher than that 3.3% (± 0.1%) degraded by Kuroshio microorganisms (2.6 ± 0.1 μM). An addition of nutrients to a similar level at 100 m depth in the SCS stimulated 11.9% (± 0.7%) of Kuroshio DOC degradation (9.6 ± 0.6 μM), indicating a co-limitation of nutrients and microbial community. Combined with the effect of active microorganism and higher nutrients level, biodegradation of extraneous DOC from Kuroshio intrusion in the SCS has the potential to contribute considerable inorganic carbon and nutrients which may regulate the carbon budget and biogeochemical processes in the SCS. Further research should be conducted to explore the coupling of environmental factors and mechanisms that control the DOC biodegradation and transformation.
Keywords: dissolved organic carbon, biodegradation, microbial community structure, nutrient, Kuroshio intrusion, South China Sea
