Effects Of Nitrogen And Phosphorus Limitation On The Chlorophyll Fluorescence And Growth Of Eight Microalgai Strains

1 Effects of nutrient and phosphorus limitation on the chlorophyll fluorescence and growth of 8 microalgal strainsThe effects of different nitrogen concentrations (0μM,100μM,880μM,7040μM) and different phosphorus concentrations (0μM,10μM,36.3μM,290.4μM) on the chlorophyll fluorescence parameters, relative chlorophyll content and cell densities of 8 microalgal strains, Tahitian Isochrysis gatbana, Isochrysis zhanjiangensis, Pavloca viridis, Chlorella sp., Nannochloris oculata, Pyramimonas sp., Nitzschia closterium f. minutissima, Phaeodactylum tricornutum are reported. The microalgae were obtained from the Microalgae Culture Center (MACC), Ocean university of China. The culture was controlled under 20±1℃, the salinity was adjusted to 31 by using distilled water, and the light intensity was 100μmol/m2·s. The main parameters determined in the present study including the maximal photochemical efficiency of PSII (Fv/Fm), the actual photochemical efficiency of PSII in the light (ΦPSII), the electron transport rate (ETR), the photochemical quenching (qP) and the non-photochemical quenching (qN,NPQ). One-way analysis of variance showed that nutrient concentrations have significant effects on the photosynthesis and growth of the 8 microalgae. Multiple comparison tests showed that the optimal nitrogen and phosphorus concentrations for the photosynthesis and growth of 8 microalgae are 880μM, 36.3μM, respectively.2 Nutrient induced fluorescence transients (NIFT) after the addition of nitrogen and phosphorusEight strains of marine microalgae, Tahitian Isochrysis gatbana, Isochrysis zhanjiangensis, Pavloca viridis, Chlorella sp., Nannochloris oculata, Pyramimonas sp., Nitzschia closterium f. minutissima, Phaeodactylum tricornutum without nitrogen or phosphorus of f/2 in natural sea water were cultured under 20±1℃, the salinity was adjusted to 31 by using distilled water, and the light intensity was 100μmol/m2·s. The algae were obtained from the Microalgae Culture Center (MACC), Ocean university of China. After 3, 5, 7 days, the limited nutrient were added into the quartz cuvette directly and the parameters F (transient fluorescence), Fm (maximal fluorescence),ΦPSII (actual photochemical efficiency of PSII in the light), ETR (electron transport rate), qP (photochemistry quenching), qN and NPQ (non-photochemistry quenching) were measured every 30s for 20min. The results showed that same tendency of decrease in fluorescence transients and increase in non-photochemistry quenching after the addition of different nitrogen sources happened among 6 strains of microalgae except Tahitian Isochrysis gatbana and Nannochloris oculata. Above all, NIFT is more obvious with the addition of NH4+-N than that of NO3--N. After phosphorus added, F, Fm,ΦPSII, ETR for 8 strains of microalgae all decreased but qN, NPQ increased.3 Recovery of chlorophyll fluorescence parameters after nutrient addition to nutrient-limited microalgae within 24hEight strains of marine microalgae, Tahitian Isochrysis gatbana, Isochrysis zhanjiangensis, Pavloca viridis, Chlorella sp., Nannochloris oculata, Pyramimonas sp., Nitzschia closterium f. minutissima, Phaeodactylum tricornutum with different nitrogen concentrations (0μM, 100μM and 880μM) or different phosphorus concentrations (0μM, 10μM and 36.3μM) of f/2 in natural sea water were cultured under 20±1℃, the salinity was adjusted to 31 by using distilled water, and the light intensity was 100μmol/m2·s. The algae were obtained from the Microalgae Culture Center (MACC), Ocean university of China. After 7 days, the lacked nutrient were added and the parameters Fv/Fm,ΦPSII, ETR, qP, qN and NPQ were measured every 2h for 24h. The results showed that Fv/Fm,ΦPSII and ETR of 8 strains of microalgae all decreased in 7 days cultivation , the degree with the increase of nutrient limitation and the length of culture time; after limited nutrient addition, Fv/Fm,ΦPSII and ETR of 8 strains of microalgae all increase but changes among qP,qN and NPQ are different because of the different microalgal strains and different kinds of nutrients.