Spatial Distribution Of Phytoplankton In Yunnan Lakes And Fragilaria Response To Arsenic Stressor

In recent decades,the intensification of human activities has led to the drama tically change of global ecosystems and biodiversity.The maintenance of ecosys tem health and diversity has become a hot issue of the whole world.lakes play an important role in providing ecosystem service,such as river regulation,shippi ng,irrigation and water supply.However,deterioration of surface water quality and degradation of ecosystem functioning have been increasingly caused by m ultiple environmental stresses,namely eutrophication and heavy metal pollution,that can also alter the spatial distribution of key lake biota and biodiversity pat tern.Yunnan Province,located at the low latitude of southwest China,is charact erized by a variety of climate types and diverse landscapes.Yunnan is home t o the a large number of species in China,serving as one of the global biodive rsity hotspots.The alpine lakes play an irreplaceable role in supporting the regio nal socioeconomic development,and provide important water resources and env ironmental basis.Lakes from the different parts of Yunnan are characterized by distinct climate feature,a long altitudinal gradient,lake typologies and catchm ent development,and thus may cause the regional heterogeneity in the distribut ion of lake biota.Moreover,Arsenic contamination has been found to be a majo r environmental problem in some of the Yunnan lakes.Arsenic pollution poses s evere risk for both lake organisms and human health,threatening the health of a quatic ecosystems.Therefore,it is urgently needed to reveal the spatial distribut ion of aquatic organisms and the response of alga to arsenic stress,so as to pr ovide important basic data for the identification of main environmental stressors and scientific basis for the biodiversity maintenance and lake restoration.In th is study,a total of 25 lakes were selected for algal surveys and regional comp arison,comprising of 13 and 12 lakes from the southeast and northwest of Yu nnan,respectively.On the basis of limnological characteristics and algal data,multivariate statistics were applied to reveal phytoplankton community structure,diversity and the environmental gradients in structuring phytoplankton.Further more,we studied the effects of arsenic on the growth,photosynthesis and antio xidant system of Fragilaria which is widespread in Yunnan.The results showe d that:(1)A total of 152 species belonging to 7 phyla and 72 genera were ident ified in 25 lakes.Chlorophyta was represented by the most species,followed by Bacillariophyta,Cyanophyta,Euglenophyta,Cryptophyta,Pyrrhophyta and Chrys ophyta,accounting for 44.1%,25.7%,17.1%,4.6%,3.9%,3.3%and 1.3%of th e total number of species,respectively.(2)The phytoplankton biomass and community structure displayed obvious spatial differences in southeast and northwest lake.The total biomass in lakes of southeast Yunnan is significantly higher than those of northwest Yunnan(t-te st;P?0.05).Phytoplankton was evenly distributed among 7 phyla,while Cyano phyta was generally dominant in southeast Yunnan.Phytoplankton community st ructure showed significant dissimilarity between the northwest and southeast in Yunnan(ANOSIM,R=0.28,P?0.01).The physical chemistry indexes,lake morp hology and PCNM were among the significant factors in driving phytoplankton distribution,accounted for 32.1%,4.6%and 2.7%of the total variance,respecti vely.(3)The algal?-diversity values in lakes of northwest Yunnan were higher than those from southeast Yunnan.The algal species richness showed a clear p attern of regional heterogeneity(t-test;P?0.05),while there was no significant d ifferences between both regions in regard to the algal?-diversity.The degree o f similarity among phytoplankton communities displayed a significant distance-d ecay relationship(R~2=0.30,P?0.001).(4)The effects of arsenate and arsenite on the growth,photosynthesis and antioxidant system of Fragilaria crotonensis and Fragilaria ulna were studied.The results showed that the toxicity of arsenite was greater than arsenate.Bot h arsenate and arsenite in low concentrations on was found to promote the alga e growth and photosynthesis,which,however,were inhibited in high concentrat ions of both arsenate and arsenite.The contents of malondialdehyde and non-e nzymatic antioxidants(glutathione)and the activities of antioxidant enzymes(to tal superoxide dismutase,catalase,glutathione reductase)were increased signific antly when both algae were exposed to higher concentrations of arsenic.