Abstract
Abstract. Bacteria recycle vast amounts of organic carbon, playing key biogeochemical and ecological roles in the ocean. Bacterioplankton dynamics are expected to be dependent on phytoplankton primary production, but there is a high diversity of processes (e.g., sloppy feeding, cell exudation, viral lysis) involved in the transfer of primary production to dissolved organic carbon available to bacteria. Here, we show the percentage of living heterotrophic bacterioplankton in the subtropical NE Atlantic Ocean in relation to phytoplankton extracellular carbon release (PER). PER represents the fraction of primary production released as dissolved organic carbon. PER variability was explained by phytoplankton cell death, with communities experiencing higher phytoplankton cell mortality showing a larger proportion of phytoplankton extracellular carbon release. Both PER and the percentage of dead phytoplankton cells increased from eutrophic to oligotrophic waters, while abundance of heterotrophic bacteria was highest in the intermediate waters. The percentage of living heterotrophic bacterial cells (range: 60–95%) increased with increasing phytoplankton extracellular carbon release from productive to oligotrophic waters in the subtropical NE Atlantic. The lower PERs, observed at the upwelling waters, have resulted in a decrease in the flux of phytoplankton dissolved organic carbon (DOC) per bacterial cell. The results highlight phytoplankton cell death as a process influencing the flow of dissolved photosynthetic carbon in this region of the subtropical NE Atlantic Ocean, and suggest a close coupling between the fraction of primary production released and heterotrophic bacterial cell survival.
Highlights
Heterotrophic bacteria play a key ecological role in the cycle of carbon and nutrients in aquatic systems (Cole et al, 1988; Fuhrman, 1992; Ducklow, 2000), being the major consumers of dissolved organic matter in the ocean (Sherr and Sherr, 1994; Azam, 1998)
Bacterioplankton dynamics are expected to be dependent on phytoplankton primary production, but there is a high diversity of processes involved in the transfer of primary production to dissolved organic carbon available to bacteria
The results presented here provide evidence of a close coupling between the heterotrophic bacterial health status and the release of recently photosynthesized carbon by phytoplankton in the NE subtropical Atlantic
Summary
Heterotrophic bacteria play a key ecological role in the cycle of carbon and nutrients in aquatic systems (Cole et al, 1988; Fuhrman, 1992; Ducklow, 2000), being the major consumers of dissolved organic matter in the ocean (Sherr and Sherr, 1994; Azam, 1998). The availability of dissolved organic carbon (DOC) is a major constraint for heterotrophic bacterial dynamics, influencing a range of processes, including heterotrophic bacteria growth efficiency, respiration or cell activity (Kirchman et al, 1991, 2004; Carlson and Ducklow, 1996; Herndl et al, 1997; Kirchman, 1997). Extracellular release or dissolved organic carbon production by phytoplankton (DOCp) is a process mostly dependent on the phytoplankton physiological state (Fogg, 1977; Sharp, 1977; Becker et al, 2014), which
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