Elevated hydrostatic pressure enhances the potential for microbially mediated carbon sequestration at the sediment–water interface in a deep-water reservoir by modulating functional genes and metabolic pathways

Abstract

Microbially mediated carbon cycling is essential for the production of refractory dissolved organic carbon and subsequent formation of stable carbon sinks at the sediment–water interface (SWI) in aquatic ecosystems, such as lakes. It remains unclear how this process is influenced by hydrostatic pressure changes due to water level fluctuation in deep-water reservoirs. Here, a microcosm simulation experiment was carried out to decipher the response of microbially mediated carbon cycling to various hydrostatic pressures (i.e., 0.1 MPa [atmospheric pressure], 0.2 MPa, 0.5 MPa, 0.7 MPa) at the SWI in Jinpen Reservoir, Shaanxi Province, China. The response mechanisms of microbial community structure, functional gene abundance, and metabolic pathway activity associated with carbon cycling were explored by metagenomics and metabolomics. Results showed that the number of microbial species in sediment samples increased with elevating pressure. The relative abundance of archaea also increased from 0.2% to 0.4% as a consequence of pressure elevation, accompanied by 0.17% and 0.03% decrease in bacteria and fungi, respectively. In contrast with low pressures, high pressures allowed the microbial communities to form a more closely connected network, which maintained more complex interspecies interactions and greater system stability. High pressures additionally improved the abundances of specific functional genes (e.g., ALDO, ACO, sdhA, and sdhC) in carbon metabolic pathways, promoted carbon fixation by the reductive pentose phosphate (Calvin) and citrate cycles, and hindered methanogenesis. Piezophilic taxa (e.g., Gammaproteobacteria, Alphaproteobacteria, Bacteroidetes) and genes (e.g., ompH, asd) were identified among carbon cycling-associated microbial communities. The piezophilic genes, which were mainly present in the Proteobacteria phylum, increased first and then decreased in abundance with elevating pressure. The findings indicate that elevated hydrostatic pressure contributes to carbon sequestration at the SWI in deep-water reservoirs by changing carbon cycling-associated microbial species, as well as relevant functional genes and metabolic pathways. Graphical Abstract