Are temperature sensitivities ofProchlorococcusandSynechococcusimpacted by nutrient availability in the subtropical northwest Pacific?

Temperature sensitivity of phytoplankton growth rate is crucial for predicting the effect of global warming on oceanic primary productivity and the efficiency of the biological carbon pump. To investigate how nutrient availability affects the temperature sensitivity of phytoplankton growth, we estimated the activation energy (E-a) of two dominant picocyanobacteria (ProchlorococcusandSynechococcus) in the subtropical northwest Pacific using short-term temperature modulated dilution experiments. We also conducted a meta-analysis on a compiled dataset of picocyanobacteria growth rate estimated by the dilution technique. Our results revealed that theE(a)ofSynechococcusgrowth rate under in situ nutrient conditions was lower than under nutrient-replete conditions. The growth response ofSynechococcusto warming could, therefore, be weaker under nutrient-limiting conditions than in nutrient-replete waters. In contrast,E(a)values ofProchlorococcusgrowth rate showed no difference between the two nutrient supply scenarios. We also found that the reducedE(a)ofSynechococcusgrowth was most likely related to the increasing trend of the half-saturation constants for growth with increasing temperature. The temperature sensitivity of half-saturation constants and the level of nutrient limitation can counteract the response ofSynechococcusgrowth rate to increasing temperature. Our results highlight the importance of considering nutrient availability when evaluating the responses of phytoplankton growth and primary production to climate warming, especially in the oligotrophic ocean.

Automated summary

Research showed that the growth response of one type of phytoplankton to warming could be weaker under nutrient-limiting conditions than in nutrient-replete waters, while the other type of phytoplankton's growth was less affected by nutrient supply scenarios. The temperature sensitivity of half-saturation constants and the level of nutrient limitation may counteract the response of one type of phytoplankton growth rate to increasing temperature.