Decoupling of bacterial production and respiration in the surface water of the North Pacific Subtropical Gyre

Heterotrophic bacterial production and respiration, two important contributors to carbon cycling, play an important role in global biogeochemical cycles. However, recent research suggests that these two processes may be decoupled, and the underlying changes in community structure and their interactions remain unclear. In this study, two research expeditions to the North Pacific Subtropical Gyre (NPSG) during the summer and winter of 2020–2021 revealed seasonal shifts in bacterial metabolism and community structure in response to environmental factors. The findings indicated notable seasonal fluctuations in bacterial abundance and production in the surface waters. Both peaked in winter compared to summer. Alterations in bacterial abundance that were further evident at the community level demonstrated significant seasonal differences in bacterial community structure and diversity and revealed, in particular, the intricacy of the networks and interactions among bacterial communities in winter. Bacterial respiration displayed no significant seasonal variations and was decoupled from bacterial abundance and production. The implication was that bacterial production did not directly dictate bacterial respiration. Specific taxa exerted a more substantial influence on bacterial respiration, potentially including groups with high respiration rates but relatively low abundance, thus challenging the notion that highly abundant taxa are invariably the most metabolically active. Moreover, the interplay between different bacterial taxa and their interactions may also impact the overall strength of bacterial community respiration. These findings significantly enhance our understanding of the decoupling between bacterial production and respiration, which is crucial for unraveling the complex mechanisms underlying carbon cycling and energy flow in marine ecosystems.