Analysis Of Phytoplankton Niche And Interspecific Association In Lakes In Cold And Arid Regions

Two kinds of ecological theories,niche and interspecific association,have been widely used to explain the structure of species community.However,most of these studies focus on land plants,and few studies have been done to quantify the niche parameters and interspecific association characteristics of phytoplankton.Nanhai Lake,a typical urban lakes in cold and arid regions,is an important wetland resource for the ecological balance in the Baotou section of the Yellow River.Phytoplankton is the indicator organism of nutrient status and ecological conditions in lake ecosystems,and the dynamic changes of its community structure directly affect the structure and function of lake ecosystem and also indirectly reflect the health status of the ecosystem.In order to investigate the phytoplankton community structure,succession rules and their relationship with habitats in Nanhai Lake of Baotou city,the phytoplankton community and physical-chemical indicators from Sep.2018 to Aug.2019 was identified and tested at 12sampling sites in Nanhai Lake.Based on the analysis of the ecological characteristics of phytoplankton community and the niche and interspecific association of dominant species,this study discussed the the dynamic changes of phytoplankton community and its correlation with habitat,which is of great significance to the ecological environment management and protection of Nanhai Lake,and can also provide reference for the study of small urban lakes in cold and arid regions.The main results are as follows:?1?A total of 173 species of 77 genera of 7 phyla of phytoplankton were identified during the study period,and most of which were mainly species in Chlorophyta,followed by species in Cyanophyta and Bacillariophyta.The seasonal alternations of species were obvious,mainly presenting a changing trend that more species were in summer and less in winter,while the spatial order of species from high to low was middle of the lake,northeast,southwest.The phytoplankton density on average was 42.93×10⁶ cells/L,and Comparatively,Cyanophyta,Chlorophyta and Bacillariophyta were the main groups to compose the quantity of phytoplankton in Nanhai Lake.The seasonal variation of phytoplankton density was basically in the shape of"V"with the lowest in winter,and the spatial variation of phytoplankton density was decreasing from the middle of the lake to the shore.The grey correlation analysis showed that the phytoplankton quantity was mainly related to the nitrogen in the lake,and the three diversity indexes indicated that the water quality of the whole Nanhai lake was moderate pollution throughout the year.Based on the analysis of dominance,15 dominant species of phytoplankton in Nanhai Lake were identified,and Aphanizomenon flosaquae,Merismopedia tenuissima and Scenedesmus quadricauda were appeared as dominant species throughout the year.?2?Calculating the niche breadth,niche overlap and niche center point of dominant species by the improved Levins Niche Breadth Index,Petraitis Index and Shi-Xiao Yu formula respectively,could determine their ecological adaptability.The result showed that the niche breadth of Aphanizomenon flosaquae in each period is relatively wide,which were evenly distributed at different sampling points and had a great chance to overlap with other dominant species.However,the niche breadth of species that were dominant species only in a certain period was narrow.Most dominant species in Nanhai Lake were aggressive,which had a development space.In addition,those dominant species that were in recession were restricted to some extent in their growing space and their niche breadth are also relatively narrow.Correlation analysis among density,dominance,niche breadth and niche overlaps showed that density of dominant species had strong relevance to the dominance,while there were no significant correlation among density and dominance of dominant species and niche overlaps.According to the value of niche center point of each dominant species in different seasons,the dominant species at the edge of ecological space showed a declining condition,and moreover,the value of the niche center point of dominant species in Cyanophyta on the one-dimensional?NH₃-N?resource axis was correspondingly higher than other phyla.?3?Using the Variance Ratio Method?VR?,?² Significance Test,the Percentage of Co-occurrence Coefficient?PC?,the Association Coefficient?AC?,and the Point Correlation Coefficients???,were quantificationally analyzed for the degree of interspecific association of dominant species.The results indicated that the phytoplankton dominant species showed a significant positive association as a whole in Nanhai Lake,and the number of species with no association was the most among the dominant pairs of phytoplankton in Nanhai Lake.Furthermore,most species-pairs in the state of association did not reach the significant level and the degree of association was low.It can be seen that even though there were more species that can depend on each other stably coexist in the habitat,there were still some species that have different needs for habitat among each other.Finally,the phytoplankton community still needs a long period of succession to form a stable community with multi-species coexistence.