Effects of Nutrient Enrichment on Organic Carbon Utilization: A Microcosm Experiment Using Long-Term Incubated Inert Waters

The ocean plays a pivotal role as a carbon sink, with microbial processes, particularly the microbial carbon pump, facilitating the transformation of dissolved organic carbon (DOC) into recalcitrant forms that support long-term carbon sequestration. This study explores the effects of nutrient enrichment on DOC utilization and microbial community dynamics through a microcosm incubation experiment using long-term incubated inert waters. We found that nutrient addition, especially in the T-4X treatment group where nutrients were added to reach four times the ambient concentrations, significantly enhanced DOC consumption. This nutrient enrichment also induced microbial community succession, favoring taxa like Bacteroidota that are known for their efficient carbon degradation. While initial increases in microbial diversity were observed, they stabilized over time. Mantel test analysis highlighted strong correlations between environmental factors, such as nitrate and microbial community structure, suggesting complex interactions between nutrient availability and microbial activity. These findings offer insights into how nutrient enrichment influences DOC cycling, microbial ecosystem dynamics, and the potential impacts of eutrophication on marine carbon sequestration processes.