Succession Of Phytoplankton Community In Beixi Reservoir Area Of Jiulong River Under Phosphorus Regulation

Phosphorus is one of the important limiting factors for phytoplankton growth.Differences in phosphorus forms and concentrations affect phytoplankton proliferation and community succession.Organic phosphorus is an important component of total phosphorus in waters,and an important source of phosphorus to promote the growth of phytoplankton.It is reported that dinoflagellate blooms mostly occur in organic phosphorus-rich waters,and Chlorophyta have more survival advantages in low phosphorus concentration environment.In the winter of 2009 and 2010,dinoflagellate blooms occurred in Beixi reservoir area of Jiulong River.In March 2018,a large increase in Dinophytas abundance was found in Beixi reservoir area of Jiulong River.To explore the competition and multiplication of phytoplankton and community succession in Beixi reservoir area of Jiulong River under organic phosphorus environment is of great significance for understanding the occurrence mechanism of dinoflagellate blooms in Beixi reservoir area of Jiulong River and early warning of prevention and control of dinoflagellate blooms.In this study,the succession of phytoplankton communities in Beixi reservoir area of Jiulong River under phosphorus regulation was explored through continuous observation and analysis in the field and simulation of phosphorus regulation.Based on the analysis of the interannual succession of phytoplankton communities and the seasonal regularity of the high biomass of dinoflagellates in Beixi reservoir area of Jiulong River,the succession of phytoplankton community and environmental factors in Jiangdong Reservoir in Beixi of Jiulong River in autumn and winter of 2018 were continuously observed and analyzed.The effects of different forms of phosphorus,phosphorus concentration and origin structure of algae on phytoplankton community succession in Beixi reservoir area of Jiulong River were studied under the condition of water temperature of 20 ? in winter.The results showed that: The high biomass of dinoflagellate in Beixi of Jiulong River mostly occurs in winter and spring.In autumn and winter of 2018(September-December),Cryptophyta and Dinophyta were the mainalgae in Jiangdong Reservoir,and phytoplankton showed succession of Chlorophyta(22.3%)and Cryptophyta(33.1%)– Cryptophyta(74.2%)– Cryptophyta(52.5%)and Dinophyta(37.0%).Total phosphorus concentration ranged from 0.09 to 0.12 mg/L,and total nitrogen concentration ranged from 1.72 to 2.36 mg/L,which was at eutrophication level.The average ratio of nitrogen to phosphorus was between 41.0 and 84.5,which was in the state of phosphorus stress.CCA analysis of phytoplankton community succession and environmental factors in Jiangdong Reservoir in autumn and winter of 2018 shows that water temperature is the main environmental factor affecting phytoplankton community succession.The results of phytoplankton community succession under high concentration of organic phosphorus(1.00 mg/L)were similar to those under inorganic phosphorus control in Beixi reservoir area of Jiulong River.When phosphorus were sufficient,the succession was mainly determined by algae provenance structure at the starting point.As well as,when the proportion of Dinophyta biomass is more than 60%,it is easy to succeed as the dominant species in the community.When the starting point of algae community structure is relatively balanced,the succession of phytoplankton community in Beixi reservoir area after two weeks has better diversity and the biomass ratios of Dinophytas(Mainly the Peridinium umbonatum var.inaequale),Cyanophyta(Mainly the Microcystis aeruginosa),Bacillariophyta,Chlorophyta,Euglenophyta and Cryptophyta were successed from 28.6 % :28.6 % :22.3 % :17.9 % :2.2 % :0.4 % to17.9 % :25.9 % :22.7 % :18.1 % :13.5 % :2.0 %.When the provenances of Dinophytas(Mainly the Peridinium umbonatum var.inaequale)reached 61.5%,Cyanophyta and Chlorophyta were 15.4% and 9.6%,respectively,the succession of phytoplankton community structure was dominated by Dinophytas(43.2%)and Chlorophyta(30.9%).When the source of Cyanophyta(Mainly the Microcystis aeruginosa)reached 61.5% and the percentage of Dinophyta and Chlorophyta was 15.4% and 9.6%,the phytoplankton community structure was dominated by Cyanophyta(59.6%)and Chlorophyta(20.4%).The succession of phytoplankton community in Beixi reservoir area of Jiulong River was similar under the control of low concentration of organic phosphorus and inorganic phosphorus(? 0.01 mg/L).The competitive advantage of Chlorophyta(Scenedesmus)was obvious when phosphorus concentration was controlled to low level,which indicated that the structure of phytoplankton community changed and toxic algae decreased after phosphorus concentration was reduced.After two weeks of low concentration of organic phosphorus culture,Phytoplankton community structure changed from Cryptophyta(54.7 %),Dinophytas(28.0 %),Bacillariophyta(4.2 %),Chlorophyta(11.9 %),Euglenophyta(1.1 %)and Cyanophyta(0.2 %)to Chlorophyta(63.7%).And the proportion of Chlorophyta in phosphorus-free medium reached 79.7%.Detection of alkaline phosphatase activity and fluorescence labeling of alkaline phosphatase showed that Scenedesmus in Chlorophyta could secrete alkaline phosphatase to utilize organic phosphorus.