Growth and Mortality Rates of Microbial Communities Respond to Experimental Warming at Different Latitudes During the Cold Season

Abstract

Abstract To evaluate the responses of microbial plankton communities to warming in coastal waters of the Pacific at different latitudes, three in situ microcosms were conducted in Taiwan and Japan during the winter of 2023. Flow cytometry was used for consecutive 7 days to monitor and analyze the microbial communities, including viruses, bacteria, and picophytoplankton (Synechococcus spp., Prochlorococcus spp., and picoeukaryotes). The control microcosms had the same natural water temperature as the coastal waters, while the others were subjected to a warming treatment of + 2–3°C. In addition, picoplankton (bacteria and picophytoplankton) growth, nanoflagellate grazing, and viral lysis rates were estimated by using modified dilution method on days 2 and 5 of the study. Our investigation revealed that the warming did not have a significant positive effect on the bacterial abundance in winter at all stations during the time-series incubations. However, a significant increase in viral abundance was observed following the temperature increase, indicating that viral impact can have a significant top-down effect on bacterial cells in our time series experiments. Furthermore, we also found that the degree of increase in viral abundance was related to picophytoplankton abundance which increased with warming at some stations in this study. Importantly, we also discovered a positive correlation between the increases in prokaryotic viral lysis and gross growth rates in the warming experiments. This suggests that increased warming in coastal water during cold seasons can potentially enhance the viral shunt, enabling the retention of carbon and energy within the microbial loop.