Phytolith Assemble Of Lake Surface Sediments And Their Relationships With Vegetation And Climate In Southwest Yunnan

Modern phytoliths and their relationship with vegetation and climate are the basis for the reconstruction of paleovegetation and paleoclimate using fossil phytoliths.With various vegetation types,southwest Yunnan is an ideal area to study modern phytoliths and their relationships with vegetation and climate.In this study,surface sediment samples were collected from 100 water bodies in Xishuangbanna,Pu'er and Lincang cities of southwest Yunnan using a clam sampler(grab)Phytolith analysis of these samples and numerical analyses,such as cluster analysis,ordination analysis,and correlation analysis,of phytolith,vegetation and observational climate data,were conducted to study characteristic of modern phytoliths and their relationships with vegetation and climate in southwest Yunnan qualitatively and quantitatively.The results are as bellow:(1)The distribution of constructive species and dominant species in modern vegetation types are consistent with the spatial distribution of major modern phytolith.This study mainly involved three vegetation types,i.e.,monsoon evergreen broadleaved forest,evergreen broadleaved forest,seasonal rain forest and semievergreen seasonal rain forest.Results of phytolith analysis on surface samples from100 water bodies in southwest Yunnan showed that the spatial distribution of modern phytolith was related to the main vegetation types.Among these phytolith assemblages,herbaceous phytolith dominated,which was followed by woody phytolith.Phytoliths of gymnosperm types were mostly distributed in the northern part of southwest Yunnan,in which phytoliths such as conifer square type and irregular cube type showed the same pattern.Among three vegetation types,phytolith assemblages in monsoon evergreen broadleaved forest and evergreen broadleaved forest were dominated by warm-type phytoliths(such as bilobate and long saddle),cold-type phytoliths(such as wavy-trapezoid,rondel,and elongate),broadleaf woody plant phytoliths(such as palmae types and “Y” type),gymnosperm woody plant phytoliths(such as irregular cubes or polyhedrons),coniferous type and other types(such as nubby-irregular shape and edges);phytolith assemblages in seasonal rain forest and semi-evergreen seasonal rain forest contained warm-type phytoliths(such as bilobate,long saddle-type,fan-type,and rectangular-type),and broadleaved phytoliths(such as palmae type).(2)This consistency between spatial distributions of major phytolith types and main vegetation types implied that major phytolith types could reflect regional vegetation and climate characteristics to a certain extent.With the increase of annual average temperature,the content of warm-type phytoliths increased from north to south.Similar patterns were also found in the spatial distributions of individual warm-type phytoliths such as long saddle,fan,and square type.Opposite trend exhibited in the spatial distribution of cold-type phytolith content,as well as individual content of coldtype phytoliths such as wavy-trapezoid,point-types,and rondel from north to south.Broadleaf woody types,“Y” types,and Palmae types were mostly distributed in monsoon evergreen broadleaved forest in the southern subtropical region.(3)The results of redundancy analysis(RDA)on major phytolith percentage data showed that the first two ordination axes explained 13.2 % of the species information and 83.7 % of the species-environment variable information.On the first RDA axis,positive scores were phytoliths of warm-type such as bilobate,cross,long saddle,and “Y” type,whereas negative scores were phytoliths of cold-type such as smooth-elongate,sinuate-elongate,point type,rondel,and wavy-trapezoid,indicating that the first RDA axis reflected the temperature gradient as showed by high correlation between the first RDA axis and mean annual temperature.On the second RDA axis,positive scores were dry-loving phytoliths such as nubby-irregular shape,point-type,smooth-elongate and sinuate-elongate,whereas negative scores were wet-loving phytoliths such as “Y” type,long saddle,and short saddle type,implying that the second RDA axis reflected the humidity gradient as showed by high correlations among the first RDA axis,mean annual precipitation,and dry season precipitation.The results of correlation analysis showed that the mean annual temperature was positively correlated with the warm-type phytolith(such as bilobate,long saddle type,and short saddle),and negatively correlated with the cold-type phytolith(such as point-type and wavy-trapezoid);the mean annual precipitation and dry season precipitation were positively correlated with wet-loving phytoliths(such as annular,pteridophyte-type,and siliceous protrusions),and negatively correlated with woody phytolith types(such as nubby-irregular shape,irregular cube or polyhedron types).Both results of RDA and correlation analysis showed that the mean annual temperature,mean annual precipitation and dry season precipitation were the main climatic factors affecting the spatial characteristics of modern phytolith assemblages in Southwest Yunnan.This study provides a necessary basis for the interpretation of paleovegetation,paleoclimate and paleoenvironment of fossil phytoliths from lakes in Southwest Yunnan.