Effect Of Environmentl Factors On Growth And Photosynthetic Physiology Of Pseudanabaena Sp.

Water eutrophication has become a global problem to be solved urgently.The outbreak of cyanobacterial bloom in recent years is a major manifestation of water eutrophication in China and even in the world.Pseudanabaena sp.is a sensitive algae species in a cascade reservoir group in South China in summer.It often blooms in this season,which seriously threatens the safety of water supply in this region.Photosynthesis is the most important physiological activity of algae.The change of chlorophyll fluorescence parameters can reflect the degree of stress on plants and is a good probe for photosynthesis.Chlorophyll fluorescence technique was used to study the effects of nitrogen and phosphorus concentration,pH,temperature and light on the growth and photosynthetic physiology of Pseudanabaena sp..The main fluorescence parameters measured in the experiment were the maximum light energy conversion efficiency（F_v/F_m）,the maximum relative electron transfer rate(rETR_max),the light energy utilization efficiency（α）and the semi-saturated light intensity（I_K）.The test results were as follows:（1）The effects of different nitrogen and phosphorus concentrations on the growth,chlorophyll fluorescence parameters and the ratio of carotenoid to chlorophyll a of Pseudanabaena sp.were investigated.Moreover,the Pseudanabaena sp.growth kinetics utilizing nitrogen and phosphorus was demonstrated through Monod equation and Droop equation.The results showed that the effects of different nitrogen and phosphorus concentrations on the growth of Pseudanabaena sp.were significant（P<0.01）.The chlorophyll a of Pseudanabaena sp.was positively correlated with nitrogen concentration ranging from 0 to 230.4 mg/L,and phosphorus concentration higher than 5.12 mg/L inhibited the growth of Pseudanabaena sp..The chlorophyll fluorescence parameters were significantly affected by different nitrogen concentrations（P<0.05）.Different concentrations of phosphorus have a significant effect on F_v/F_m,I_K and have no significant effect on rETR_max,α（P>0.05）.Pseudanabaena sp.could increase rETR_max,αto resist adversity when nitrogen and phosphorus were limited.K_sP is far less thanK_sNwhich proven that Pseudanabaena sp.has better affinity for phosphorus.The minimum share of intracellular phosphorus for Pseudanabaena sp.is0.0486μg/mg,under which the proliferation of algal cells will cease.The ratio of carotenoid to chlorophyll a is negatively correlated with the concentration of nitrogen and phosphorus.Alkaline phosphatase activity（APA）was negatively correlated with phosphorus concentration.（2）The growth and chlorophyll fluorescence parameters of Pseudanabaena sp.were studied in the range of pH 3-13.The experiment was divided into 2 groups.One group measured the actual pH every day and then adjusted the pH to the initial set value.The other group adjusted the pH to the set value at the beginning of the experiment and did not adjust it artificially.The results showed that the Pseudanabaena sp.preferred the alkaline environment and had a strong adjustment and adaptation to the water pH.In the unartificially control pH test,the pH 5-11 test groups pH tended to 10.9-11.5,In the artificially control pH test,the pH 7-11 test groups pH tended to 9.5-11.3.The test group that regulated pH to 11 per day had a best growth condition,Pseudanabaena sp.could not grow when pH was 3 and 13.In the unartificially control pH test,F_v/F_m and rETR_maxax were positively correlated with pH in the range of 5-11,the I_K of pH 7 test group increased significantly in the later stage of experiment.F_v/F_m and rETR_maxax in the pH 11 treatment group were significantly higher than those in other treatment groups.（3）The effects of light intensity on chlorophyll a content,OD₆₆₅,chlorophyll fluorescence parameters and carotenoid content of Pseudanabaena sp.in the range of500-2500 lx were studied.Light intensity had significant effect on chlorophyll a content,OD₆₆₅,α,rETR_max,I_K and carotenoid content of Pseudanabaena sp.（P<0.05）,but no significant effect on F_v/F_m（P>0.05）.The most suitable light intensity for Pseudanabaena sp.is 1500 lx.With the increase of cultivation days,αand rETR_maxax were negatively correlated with light intensity,I_K was negatively correlated with light intensity,which indicated that Pseudanabaena sp.could resist low light stress by improving light energy utilization efficiency.With the increase of light intensity,the tolerance of Pseudanabaena sp.to light intensity increased.The relative content of carotenoids in 2500 lx test group was significantly higher than that in low light intensity test group.（4）The effects of temperature on the growth and chlorophyll fluorescence parameters of Pseudanabaena sp.were studied in the range of 15-35℃.Temperature had a significant effect on the growth and chlorophyll fluorescence parameters of Pseudanabaena sp.（P<0.05）.During the 1-13 days,the chlorophyll a content in the range of 15-30℃was positively correlated with the temperature.After 13 days,the growth rate of the 30℃test group decreased significantly.The optimum temperature of Pseudanabaena sp.was 25℃,the growth of Anabaena pseudoranthus was significantly inhibited at 15℃and 35℃.The chlorophyll fluorescence parameters of35℃test group were significantly lower than those of the other test groups and did not recover during the experiment.With the increase of culture days,the F_v/F_m,αand rETR_maxax of the 15℃test group gradually returned to normal values.