Research On The Effects Of Plankton Species Diversity On Community Productivity And Stability

The eutrophication of water has become one of the greatest threats to most freshwater ecosystems and coastal marine ecosystems in the world.Eutrophication causes rapid fluctuations of planktonic biomass in water,which also leads to the loss of species diversity and affect the normal function of aquatic ecosystems.Current reasearch has shown that plankton biodiversity has a critical impact on ecosystem function.However,the influence and mechanism of plankton biodiversity on community productivity and stability in natural aquatic ecosystems are still controversial.In this research,phytoplankton community was investigated seasonally from 2012 to 2014 in Lake Dongping.Through three kinds of diversity indicators yield-coefficient and scaling coefficient,we explore the mechanism of diversity impact on productivity and stability.The results of the present research will be helpful in understanding the influence of diversity on ecosystem function in freshwater lakes.The main results are as follows:(1)A total of 129 phytoplankton species belonging to 45 genera and 8 phyla was identified in Dongping lake.The phytoplankton community included 50 Chlorophyta species,21 Bacillariophyta species,37 Cyanophyta species and 11 Euglenophyta species.Mean phytoplankton density varied from 6.313 × 105 ind./L to 51.7×105 ind./L.The cell density of Chlorophyta and Cyanophyta were more sensitive to seasonal changes,while the cell density of Bacillariophyta and Euglena had no significant difference in four season.The cell density in 3,4 and 7 sites were lower than that in other sites.The biomass of phytoplankton ranged from 0.44 mg/L to 5.46 mg/L.The minimum was reached in winter.(2)The species richness of total phytoplankton was significantly correlated with biomass in different seasons.The species richness of Chlorophyta,Cyanophyta and Euglenophyta was positively correlated with community biomass in four seasons.The community productivity increased apparently with increasing the number of functional groups in four seasons.The yield coefficient of most algas were higher than 1,which indicates that species diversity had a positive effect on community productivity.Species richness,the number of functional groups and NH3-N were the most significant factors that influenced phytoplankton,and phytoplankton species diversity has a dominant impact on productivity.(3)The relationship between phytoplankton species richness and community turnover stability varied in different seasons:in summer and winter,there was a positive relationship between the two variables.The functional group diversity had a strong influence on community turnover stability in summer and winter.The evenness of phytoplankton had a weak impact on community turnover stability.Seasonal changes made the relationship of the two variables become more complex.From summer to autumn,species richness was positively correlated with community turnover stability.From autumn to winter,the two variables had a "U-shaped" relationship.The scaling coefficient of most algas ranged from 1 to 2,indicating that species diversity had a positive effect on TSI notably.Results of CCA revealed that NH3-N,WT,and evenness were principal factors affecting the temporal stability of phytoplankton.Results in this study will be helpful in understanding the impact of plankton diversity on ecosystem function in freshwater,and will provide a beneficial guidance for protecting biodiversity and maintaining the healthy development of ecosystems.