Terrigenous organic carbon contributes to reservoir carbon emissions: Potential role of the microbial community along a trophic gradient

Abstract

Freshwaters are important carbon sources to the atmosphere and are influenced by different sources of organic carbon (OC). Microbial community is a crucial trophic network driving carbon cycling in the aquatic ecosystems. Yet, whether and how their interactions affect carbon cycling and emissions in the reservoir remains unclear. Here, we explored the interactions between phytoplankton and bacteria in reservoirs along a trophic gradient. An increase in the trophic state intensified the interaction between phytoplankton and bacteria communities. Their diversity and niche breadth indexes both decreased. Such intensification was contributed not only by the input of nutrients triggering an increase in trophic state but also by the bulk input of terrigenous OC, shaping the concentrations of CO2 and CH4 in the water phase and their air-water fluxes along the trophic gradient. Upon this, a conceptual framework was proposed to explain the positive/negative feedback of phytoplankton-bacterial interactions to carbon emissions, projecting the dual regulation of aquatic ecosystems and carbon dynamics along a trophic gradient.