Photosynthetic characteristics and inferred changes in thylakoid membrane fluidity determine bloom succession between Anabaena and Microcystis in eutrophic lakes

Abstract

Anabaena and Microcystis are common dominant cyanobacterial genera and frequently form blooms in large shallow eutrophic lakes in China. There is usually a quick succession between these two cyanobacterial blooms in early summer; however, there is currently no solid evidence based on photosynthesis and population competition to explain this phenomenon. This study compared the photosynthetic parameters and the indirectly measured thylakoid membrane fluidity characteristics between Anabaena and Microcystis. The results showed that the growth rate, the maximum photochemical efficiency of PSII (F v/F m), and the maximum relative electron transport rate (r ETR max) of Microcystis cultured at 25 °C were significantly lower than those from cells grown at 15 °C, indirectly suggesting a marked limitation of thylakoid membrane fluidity at low temperatures. Chlorophyll fluorescence dynamics also indicated inhibition of NPQ formation and membrane fluidity when Microcystis was cultured at low temperatures; however, this inhibition was not significant for Anabaena. Fourier transition infrared (FT-IR) spectrometry indicated that the thylakoid membrane of Anabaena can maintain homeostasis fluidity through the upregulation of unsaturated fatty acids when exposed to chilling stress. Increasing the temperature significantly promoted the growth rate of Microcystis, while it had little effect on Anabaena. Moreover, photoinhibition of Anabaena was more easily induced by high light, thus accelerating the bloom succession from Anabaena to Microcystis during warm seasons. An activation-energy model was used to deduce that the threshold temperature of bloom succession was 15.4 °C, which would increase to 16.2 °C and decrease to 14.9 °C under conditions of N-limitation and P-limitation.