Temporal And Spatial Patterns Of Diatom Diversity In Typical Peatlands In The Monsoonal Region Of Eastern China

Peatlands are a significant carbon sink in the world.As a limno-terrestrial transition ecosystem,peatlands host many rare species,and hence peatlands are of great significance to mitigate global climate change and to protect biodiversity.Diatoms are important primary producers in aquatic environment.Compared with extensive investigations of diatom diversity in lakes and rivers,limited knowledge is available on diatom biodiversity in peatlands at present.In this study,our aims are to compare diatom diversity patterns and the underlying driving forces in Sphagnum peatlands of central and northeastern China,to disentangle the effects of local environment,regional climate and spatial factors on the species composition.Secondly,based on the seasonal monitoring data of diatoms and environmental factors in Dajiuhu Peatland,seasonal variations of diatom assemblage and biodiversity are investigated.Furthermore,based on sedimentary diatom records in a peat core,in combination with sedimentary records of carbon and nitrogen and paleoclimate data,this thesis explores the mechanisms for the variations in diatom assemblage and diversity in Dajiuhu Peatland over the past 150years.Major conclusions are listed as follows:（1）A total of 200 diatom species were observed in 138 surface Sphagnum samples collected from eight peatlands in northeastern and central China.310 diatom species,belonging to 71 genera,were observed in 134 seasonal monitoring samples collected from Dajiuhu Peatland.In addition,89 species belonging to 26 genera were identified in the sediment core of Dajiuhu Peatland.Diatom assemblages are dominated primarily by the genera of Eunotia and Pinnularia,which prefer lightly acidic environments.The most abundant species include Eunotia paludosa,Eunotia minor,Eunotia mycophila,Frustulia saxonica,Pinnularia microstaron,Pinnularia subcapitata,etc.（2）Diatom species richness and beta diversity are higher in central China than in that of northeastern China,probably due to strong dispersal limitation in these enclosed montane peatlands of central China.The Simpson index was negatively correlated with dissolved organic carbon in central China,while it was negatively correlated with water table depth（WTD）in northeastern China.For diatom composition in the two regions,the pure effect of environmental variables explained more variance than that of regional climate or spatial factors,suggesting that niche-based processes primarily determined diatom composition in these peatlands.（3）Diversity index of diatoms in Dajiuhu Peatland varied among spring（34samples）,summer（50 samples）and autumn（50 samples）,while the dominant genera and species were relatively stable.From spring to summer and autumn,the relative abundance of the dominant diatom taxa,E.paludosa,gradually decreased,concurrent with the increases in other diatom species and species richness.Diatom assemblages were significantly correlated with precipitation,WTD and physicochemical parameters,while species diversity was significantly related to precipitation and air humidity.（4）Diatom assemblages of a 42 cm long peat core in Dajiuhu Peatland documented the history of regional environmental changes over the last 150 years.Diatom assemblages were dominated by F.saxonica in the bottom layers,while diatom flora shifted to the community co-dominated by E.minor and E.paludosa since the 1970s,and F.saxonica increased to be the sole dominant species from the early 21^stcentury.Results of redundancy analysis and correlation analysis,variations in diatom assemblages and diversity were significantly correlated with temperature,summer rainfall and C/N ratios.Diatom assemblages and diversity index mainly responded to climate variability before the 1970s,and then hydrological regulation and subsequent vegetation succession（sources of organic matter）were the major driving forces.