Reconstruction Of The Succession Of Bloom-forming Cyanobacterial Community By Sedimentary Ancient DNA Records And Analysis Of The Driving Factors In Erhai Lake

Cyanobacterial bloom is a common ecological disaster in eutrophic lakes.Replacement of dominant species in cyanobacterial bloom is a common phenomenon,but its driving factors are not clear.For example,according to the report that the dominant species of water-bloom of cyanobateria in Erhai Lake were successionated Aphanizomenon-Anabaena-Microcystis,from 1950 to 2013.Due to the lack of long-term observation data including continuous ecological investigation and literature,like the Erhai Lake water quality in good condition(Ⅱ-Ⅲ class)under the law of cyanobacterial blooms and the mechanism of succession of dominant species of cyanobacteria is unknown.In order to understand the succession process and its driving factors,this study used the method of paleolimnology combined with molecular biology and high-throughput sequencing technology to reconstruct the succession process of cyanobacterial community in the past 100 years in Erhai Lake.The method of reconstructing community succession by algae ancient DNA was established by simulating sedimentary condition analysis.The sediment column were collected from Erhai and were finely divided and then analyzed by 210Pb/137Cs,Radiometric dates were calculated using the constant rate of supply(CRS)210Pb dating model.The abundances of total Cyanobacteria,Microcystis,Dolichospermum,and Aphanizomenon,estimated by qPCR,in the sediment DNA samples,as well as to the samples of cyanobacterial 16s rRNA genes with high throughput sequencing analysis.The geochemical indicators in sediments were determined,and at the same time,climate change data in the historical period was collected,analysingthe relationship between succession of cyanobacteria community and environmental variables.The main results of study on the characteristics of simulated algae ancient DNA degradation are summarized as following:1.The DNA degradation rate of Microcystis aeruginosa,Melosira varians and Chlorella pyrenoidosa under the condition of 10℃ below under the condition of 20℃(p<0.05).The DNA degradation rate of Melosira varians higher than Microcystis aeruginosa and Chlorella pyrenoidosa(p<0.05),the differences between Microcystis aeruginosa and Chlorella pyrenoidosa were not significant.The residual law of the same species with different initial concentration is consistent after the same degradation time.The degradation rate of different algae species is different.2.The DNA degradation rate of Microcystis aeruginosa tends to be stable from the 75 th day under the condition of 10℃ and 20℃.The DNA degradation rate of Melosira varians tends to be stable at the 75 th day under the condition of 10℃ and under the condition of 20℃ at the 44 th tends to be stable.The DNA degradation rate of Chlorella pyrenoidosa tends to be stable at the 197 th day under the condition of 10℃ and under the condition of 20℃ at the 167 th tends to be stable.The main results of reconstruction of the succession of bloom-forming cyanobacterial community by sedimentary ancient DNA records and analysis of the driving factors in Erhai Lake are summarized as following:1.It successfully reconstructed the succession process of dominant species of cyanobacteria in Erhai Lake during the past 100 years(ca.1902-2010 AD)by using qPCR technique to amplify the target genes in ancient DNA.From 1902 to 1975 AD,Aphanizomenon was the dominant species,and the abundance of Dolichospermum was low.From 1975 to 1999 AD,both Microcystis and Dolichospermum increased by 3 orders of magnitude,and the abundance of Aphanizomenon decreased.From 1999 to 2010 AD,the abundance of Dolichospermum decreased,and the abundance of Microcystis increased continuously which becoming the absolute dominant species in Erhai Lake.2.The results of RDA analysis show that total population,the tourist population,the EF-Zn and the TP(%)in sediments are the main factors affecting the succession of the total Cyanobacteria and Microcystis communities(p<0.01,n=19).The total population and annual range of water level are the main factors affecting the succession of the Dolichospermum community(p<0.01,n=19).3.The results of variation partitioning analysis show that human impact and climate proxies independently explained 60.7%and 2.9%of the abundance change of cyanobacteria,respectively,and the interaction between climate change and human impact accounted for 12.5%,thus anthropogenic activity impact is the main factor affecting the succession of cyanobacteria in Erhai Lake.In conclusion,Cyanobacteria,Chlorophyta and Diatoms showed different rates of degradation at different temperatures.The residual law of the same species with different initial concentration is consistent after the same degradation time.The degradation rate of different algae species is different.From 1902 to 1975 AD,Aphanizomenon was the dominant species,and the abundance of Dolichospermum was low.From 1975 to 1999 AD,both Microcystis and Dolichospermum increased by 3 orders of magnitude,and the abundance of Aphanizomenon decreased.From 1999 to 2010 AD,the abundance of Dolichospermum decreased,and the abundance of Microcystis increased continuously which becoming the absolute dominant species in Erhai Lake.