Research On The Growth And Photosynthesis Of Chlorella Vulgaris Under Different Nitrogen And Phosphorus Concentrations

The problem of increased eutrophication potential caused by excessive nutrients in reclaimed water was widely concerned.The main causes of eutrophication were suitable temperature,slow flow regimes,and relatively abundant nutrients such as total phosphorus and total nitrogen,which could provide aquatic plants?mainly algae?with a rich material basis,which could result in the phytoplanktonic algal blooms.Through the promotion of photosynthesis,algae used carbon dioxide,water,nitrogen and phosphorus to produce its own protoplasm,and the basic reason for algal blooms was the concentration of nitrogen and phosphorus increased.Chlorophyll fluorescence analysis technology was a kind of new plant living body measurement and whose diagnosis technology was based on photosynthesis theory,and the body chlorophyll was used as a probe to study and detect the photosynthetic physiology and various external factors of plants.In order to deeply understand the suitable growth and photosynthesis environment conditions of Chlorella vulgaris,studying the effect of nutrients on the growth and chlorophyll fluorescence of Chlorella vulgaris was conducive to the assess of eutrophication and predict and prevent the occurrence of blooms and red tides,and then provide a certain theoretical basis.In this study,Chlorella vulgaris was selected as the research object,the interaction experiments of different levels of phosphorus and nitrogen were set combined with the secondary effluent and surface water environmental quality standards,the growth indexes and nutrient utilization of Chlorella vulgaris under different concentrations of nitrogen and phosphorus were determined.Meanwhile,the Imaging-PAM chlorophyll fluorescence imaging system was used to determine the effect of different nitrogen and phosphorus concentrations on the main chlorophyll fluorescence parameters of Chlorella vulgaris.The main chlorophyll fluorescence parameters were maximum photochemical efficiency?F_v/F_m?,electron transport rate?ETR?,non-photochemical quenching?NPQ?,photochemical quenching?qP?.The results showed that within the the optimal phosphorus concentration(NO₃^--N:1⁸ mg/L;PO₄^3--P:0.2¹.0 mg/L)for the growth of Chlorella vulgaris was 0.4mg/L,and phosphorus was the main limited factor for the growth of Chlorella vulgaris when phosphorus concentration was less than 0.4mg/L,while nitrogen was the main limited factor for the growth of Chlorella vulgaris when phosphorus concentration was higher than 0.4 mg/L.The maximum density of common chlorophyll was 5×10⁶⁷×10⁶cells/mL,the maximum content of chlorophyll a was 2.05 mg/L,and the absorption rates of nitrogen and phosphorus were 56%⁹8%and 89%¹00%,respectively.Under the low phosphorus condition,the algae density,the absorption rate of nitrate nitrogen and the chlorophyll a concentration increased with the increase of the initial phosphorus concentration.When the phosphorus concentration was fixed,the maximum photoenergy conversion efficiency?F_v/F_m?of PS?reaction center increased with the increase of nitrogen concentration;and the F_v/F_m and electron transfer rate?ETR?tended to increase firstly and then decreased?or stabilized?with the extension of culture time.When phosphorus concentration was 0.2 mg/L,Chlorella vulgaris was under the phosphorus stress,and the algal density,chlorophyll a concentration and F_v/F_m were significantly lower than other concentration.And F_v/F_m reduced to 0.18⁰.24,which considered to be the threshold value for Chlorella vulgaris under the phosphorus stress.The low phosphorus concentration has a significant influence on Chlorella vulgaris.Under the initial phosphorus concentration of 0.2 mg/L,F_v/F_m of Chlorella vulgaris was lower;algal density and chlorophyll a concentration was rapidly decreased than other conditions;and the ability of cell division and photosynthetic activity of Chlorella vulgaris reduced sharply.Under other phosphorus concentration?0.4,0.5,and 1 mg/L?,F_v/F_m value of Chlorella vulgaris was at a higher level and decreased slowly with the change over time,and the cell density and pigment content showed slightly drop.Therefore,the F_v/F_m value under low phosphorus concentration was highly correlated with the biomass and nitrogen and phosphorus utilization of Chlorella vulgaris,which could be used to comprehensively characterize the growth status of algae and to study the nutrient stress of microalgae.