The Effect Of Environmental Factors On The Growth And Chlorophyll Fluorescence Characteristics Of Two Red Tide Algaes

Phytoplankton is the primary producer of aquatic ecosystem and has a special niche in aquatic ecosystem.The phenomena of phytoplankton explosive proliferation in a short time were called algal blooms?water blooms in freshwater;red tides in ocean?.Some phytoplankton contained toxins or could secrete mucus which harmed to secondary producers or other consumers and destroied the marine ecological balance.Due to the increasing frequency of red tides caused by nutrient releases,red tides of Prorocentrum donghaiense and Skeletonema costaum occured frequently in the coastal areas of Zhejiang Province and the Changjiang Estuary.They becomed one of the dominant algae species in the East China Sea.Phytoplankton synthesizes organic matter through photosynthesis.Photosynthesis was the most basic and important physiological characteristic of phytoplankton.It was extremely sensitive to the changes of environmental factors.The limitation of environmental factors had an effect on the termination of red tide.Each step of photosynthesis is closely coupled.Any change could affect the photosystem II?PS??and cause fluorescence changes.Therefore,chlorophyll fluorescence could be used to detect all changes of photosynthesis process easily and quickly.In order to understand the effects of temperature,light,phosphate and their interactions on the growth and chlorophyll fluorescence characteristics of Prorocentrum donghaiense and Skeletonema costaum.Each environmental factor set three levels(Temperature:17,23,29?;Light:80,120,160?mol photons m^-2 s^-1;Phosphate:0.1,1,10?mol/L).Using L18?37?orthogonal experimental table and considering interactions between two environmental factors to study the changes of chlorophyll a concentration and chlorophyll fluorescence characteristics of Prorocentrum donghaiense and Skeletonema costaum by indoor culture experiments.The results were as follows:1.Prorocentrum donghaiense had a higher concentration of chlorophyll a and a faster photosynthesis rate where the condition is the 17-23?,80-120?mol photons m^-2 s^-1 and 10?mol/L.The optimal horizontal combination of environmental factors was 23?,80-120?mol photons m^-2 s^-1 and 10?mol/L.Phosphate had the most significant effect on the peak value of chlorophyll a?P<0.01?.Light,temperature and the interaction between temperature and phosphate had a significant effect on the peak value of chlorophyll a?P<0.05?.The interaction between temperature and phosphate on chlorophyll a peak value had a significant impact when phosphate was 10?mol/L and temperature was 23?.The chlorophyll a of Prorocentrum donghaiense could maintain a stable and slow rise when phosphate was 1?mol/L,temperature was 17-23? and light was 80-120?mol photons m^-2 s^-1.When the temperature was 17-23?,light was 80-120?mol photons m^-2 s^-1,it was found that the 10?mol/L experimental groups' ?,rETRmax and IK were higher than the 1?mol/L experimental groups,but the Fv/Fm was slightly lower than 1?mol/L experimental groups by comparing the chlorophyll fluorescence parameters of nutrients were continuously replenished or highly eutrophic waters and sea area with high incidence of red tide.This indicated that the photosynthetic rate of Prorocentrum donghaiense was higher at 10?mol/L phosphate concentration and photosynthetic activity was higher at 1 ?mol/L phosphate concentration.2.Skeletonema costaum could reach a higher level under high phosphates?10?mol/L?.And the optimum combination of environmental factors was 23?,120?mol photons m^-2 s^-1 and 10?mol/L.Phosphate had a significant effect on the peak value of chlorophyll a of Skeletonema costaum during culture?P<0.01?.Temperature,light and the interaction between environment factors had no significant effect on the peak value of chlorophyll a concentration?P>0.05?.The photosynthetic activity of Skeletonema costaum was higher at 10?mol/L phosphate concentration,but the light use efficiency a did not show significant difference with phosphate concentration.The Fv/Fm was significantly affected by light when phosphate concentration was 10?mol/L and 1?mol/L?P<0.05?.When phosphate concentration was 10?mol/L,F_v/F_m was lower at 160 ?mol photons m^-2 s^-1 light intensity and higher at 80,120?mol photons m^-2 s^-1.When phosphate concentration was 1?mol/L,Fv/Fm was the lowest at 120?mol photons m^-2 s^-1 light intensity.In this paper,the effects of environmental factors and their interaction on the growth of Prorocentrum donghaiense and Skeletonema costaum were discussed by using chlorophyll a and chlorophyll fluorescence parameters.The optimum combination of temperature,light and phosphate for the growth of Prorocentrum donghaiense and Skeletonema costaum were obtained.The changes of photosynthetic activity of Prorocentrum donghaiense and Skeletonema costaum under the optimum conditions and the possible outbreak of red tide were explored,which laid a foundation for the outbreak mechanism of red tide of Prorocentrum donghaiense and Skeletonema costaum.