Temporal And Spatial Pattern Changes And Key Driving Factors Of Phytoplankton Diversity In Jingpo Lake

Phytoplankton in freshwater lakes are primary producers and play an important role in the cycling of matter and conversion of energy in the ecosystem,and influence the function and structure of the overall ecosystem.Phytoplankton have a short growth cycle and can respond rapidly to environmental changes.Thus,the dynamics of their community structure can reflect the quality and health of freshwater ecosystems.Jingpo Lake is located in Mudanjiang City,Heilongjiang Province.Jingpo Lake is the largest volcanic barrier lake and a national scenic area in China.And it is one of the important fresh water resources in Mudanjiang basin.In this study,phytoplankton samples were collected and processed at 34 sampling sites in the Jingpo Lake by season,from 2017 to 2019,2021（autumn）.The species composition,functional group succession,diversity indices,and dominant species distribution of phytoplankton in Jingpo Lake during four years was studied systematically.The spatial and temporal changes in phytoplankton community structure and its response to environmental factors were analyzed.Further,based on the ecological characteristics of phytoplankton communities in the Jingpo Lake,the ecological niches of dominant species between the dynamics of phytoplankton communities are explored.The applicability of different evaluation systems in lake health evaluation was also analysed along with the results of the physical and chemical monitoring of water quality.We applied high-throughput（23S r DNA sequencing technology）and microscopic morphological identification to supplement the species diversity of microalgae in Jingpo Lake and established a phytoplankton diversity database.Therefore,the results obtained in this study provide a reference for the restoration of volcanic barrier lake ecosystems and biodiversity conservation in northeast China,and they are presented below.（1）In total,271 taxonomic units of phytoplankton（belonging to 99 genera of 39families of 22 orders of 10 classes of 8 phyta）were identified during the four-year study period in Jingpo lake.We found that diatom and green algae were the largest and second largest in numbers,respectively.The ecological type of the Jingpo Lake is a diatom-cryptophyte algae type in 2017.In 2018,it became diatom-cyanobacteria-green algae type.The diatom-cyanobacteria type succeeded in 2019.In autumn of 2021,the diatom-cyanobacteria-green algae type succeeded again.Phytoplankton abundance showed obvious spatial and temporal patterns in Jingpo Lake.Finally,the spatial and temporal distributions of the three functional phytoplankton groups（FG,MFG and MBFG）in the Jingpo Lake were clearly.（2）The study of phytoplankton diversity indices showed that the spatial and temporal distribution of the Margalef（H）,Shannon-Wiener（H’）diversity indices,Pielou（J）evenness and Simpson’s（D）diversity indices is obvious.There are abundant species and stable community structure of phytoplankton in Jingpo Lake.The diversity index was used to evaluate the water quality of Jingpo Lake.The results showed that the main water body of Jingpo Lake was in a moderately polluted and eutrophic state.（3）We also detected clear spatiotemporal patterns in the physicochemical properties of water in the Jingpo Lake,with significant seasonal variations in dissolved oxygen（DO）,conductivity（Sp Cond.）,permanganate index(COD_Mn),p H,water temperature（WT）,turbidity（Tur.）,total nitrogen（TN）and total phosphorus（TP）。The significant Interannual variations in Sp Cond.,COD_Mn,p H,TP,DO,TN and Tur.and significant spatial variations in Sp Cond.,Tur.,DO,TN and TP.We also identified certain correlations between the physicochemical factors.RDA showed that environmental variables WT and Tur.were the key driving factors affecting phytoplankton community in Jingpo Lake during the study period.The results of TLI showed that the water quality of Jingpo Lake was at the mesotrophic levels.（4）Melosira granulate,Ulnaria ulna,Cryptomonas erosa,Crucigenia rectangularis,Ankistrodesmus angustus,Pseudanabaena limnetica,Aulacoseira pusilla and Aphanizomenon flos-aquae being the dominant phytoplankton species during the study period.The ecological niche widths of dominant phytoplankton species have certain seasonal differences,most of the dominant species had high niche widths only in one or two seasons.Although there appeared to be comparatively limited niche overlap among them and interspecific competition was weak in Jingpo Lake.Consequently,the phytoplankton community tended to remain stable,with a certain degree of independence among species.（5）Using high-throughput sequencing technique to analyze samples,combination with morphological observation,ultraplankton（Thalassiosira,Synechococcus）not observed in morphological identification were added.This study provided important information for analyzing the species and abundance of phytoplankton communities in different spaces of Jingpo Lake,and further clarified the characteristics of phytoplankton biodiversity in Jingpo Lake.