Effects Of Environmental Stress On The Chlorophyll Fluorescence Of 4 Microalgal Strains

The modulate chlorophyll fluorescence kinetics of 4 microalgal strains (Phaeodactylum tricornutum, Chaetoceros gracilis, Isochrysis galbana 3011 and I. galbana 8701) under environmental stress(salt, temperature, heavy metals) were investigated. The main parameters determined in the present study including the maximal photochemical efficiency of PSII (F_v/F_m), the potential activity of PSII (F_v/F_o), the actual photochemical efficiency of PSII in the light (ΦPSII=yield), the relative electron transport rate (rETR), photochemical quenching (qP) and non-photochemical quenching (NPQ).(1) Changes in the fluorescence parameters, cell density and chll content were investigated in the 4 microalgal strains during exposure the cultures to different salinity (1-90) for different time(12h, 24h and 48h) with Water-PAM chlorophyll fluorometer. The results showed that, the parameters F_v/F_m, F_v/F_o,ΦPSII, rETR and qP decreased in 4 strains of microalgae, while NPQ significantly increased in P. tricornutum, C. gracilis and I. galbana 3011, but first increased then decreased in I. galbana 8701 under salt stress. The cell density and chlorophyll fluorescence of 4 microalgal strains were also decreased under salt stress. F_v/F_m, F_v/F_o,ΦPSII, rETR , cell density and chll content all showed significant correlations with salinity, the pattern and strength of the correlations varied with salinity range and microalgal strains. Moreover, there are significant positive correlations between fluorometer parameters(F_v/F_m, F_v/F_o,ΦPSII, rETR and qP) and cell density, as well as between chll content and cell density. The optimum salinity ranges of the above 4 microalgal strains were 20, 20-30, 10 and 30, respectively.(2) The chlorophyll fluorescence parameters of the above 4 microalgal strains under high temperature stress(35-50℃) were investigated with Water-PAM chlorophyll...