Photochemical responses of phytoplankton to rapid increasing-temperature process

Phytoplankton is sensitive to rapidly increasing temperature in spring. However, studies on the effect of temperature on phytoplankton have mainly focused on constant temperatures. It is necessary to clarify the determining parameters of phytoplankton shifts during temperature increases, as temperatures are predicted to fluctuate more intensively and frequently in the future. In the study, we analyzed the responses of photosynthetic properties and growth in a cyanobacterium (Microcystis aeruginosa) and a green alga (Chlorella pyrenoidosa), the dominant species in Taihu, to rapid increasing-temperature process in the laboratory and in the field. The results show that gradually increasing temperature inhibited photosynthesis and the growth of C. pyrenoidosa and had almost no effect on M. aeruginosa. Elevated increasing temperature range also had more significant effects on the photosynthetic properties and growth rates of C. pyrenoidosa than those of M. aeruginosa in the laboratory and in the field. All of these results suggest that the photosynthetic performance of M. aeruginosa is more suitable to gradually increasing temperature and relatively strong temperature variations than that of C. pyrenoidosa, which might partially contribute to Microcystis excluding Chlorella competitively in aquatic ecosystem. Our findings point out the possible importance of the rapid and dramatic increasing-temperature process to the formation of cyanobacterial blooms.