The variation of the relative abundance of C_3/C_4 plant in terrestrial vegetation since the Last Glacial Maximum(LGM) and its driving mechanism is a key research question in paleoecology.However,there is a lack of record based on the relative abundance of C_3/C_4 plant from southern part of China,particularly the high resolution paleoclimate records are sparse.Whether climate and/or atmospheric CO_2 concentration are the most important driving factors for these changes remain to be elucidated.Black carbon or elemental carbon is produced by incomplete combustion of biomass and fossil fuels.Due to the inert characteristics of the elemental carbon,effect on the photochemical and microbial reactions after deposition can be negligible.Therefore black carbon can be well-preserved in the sediments for a long period of time.During the process of combustion,different isotopic fractionation effect exhibits as the chemical composition of biomass varies.However,the variation in the carbon isotopic composition (delta~(13)C_(EC)) is relatively small when compared to the plant delta~(13)C.In the past few years,there has been increasing attention received on developing the method that uses delta~(13)C_(EC) to reconstruct vegetation and climate change from lacustrine sediments.In this study,a 684-cm sediment core (25°51.02'N,100°11.02'E) was recovered at the depth of 13.5m of Erhai Lake (25°25'~ 26° 16'N,99°32'~100°27'E),Yunnan Province.The core was sub-sampled at 4cm intervals and a total of 171 carbon isotope (delta~(13)C_(EC)) samples were analyzed throughout the record.The relationship between the relative abundance of C_3/C_4 plant and the paleoenvironmental changes from Erhai Lake,Yunnan Province was investigated.The record covers periods since 19.4cal.ka B.P.to the present and is based on the analysis of elemental carbon delta~(13)C_(EC) and AMS radiocarbon (~(14)C) dates using 13 plant remains and charcoal samples from the lake sediment.The results show that during the LGM,the composition of vegetation around Erhai Lake catchment contains a mix of C_3 and C_4 plants,and C_4 plant is the dominant type during this period.The relative abundance of C_4 plant decreased abruptly since 14.7cal.ka B.P.and has reached the minimum abundance in the Early Holocene.In the Late Holocene,the C_4 plant shows an expansion to some degree however,the overall composition of vegetation is still dominated by C_3 plant.This delta~(13)C_(EC) record from Erhai Lake is consistent with the relative abundance of C_3/C_4 plant recorded in other marine and lake sediments in the low latitudes.These records all together suggest that the abundance of C_4 plant is relatively high and dominant the vegetation composition during the LGM.In addition,the C_4 plant in the Erhai Lake catchment also shows significant expansion around 15.7cal.ka B·P.,12.Ocal.ka B.P.,8.Ocal.ka B.P.and 5.Ocal.ka B.P.These abrupt changes were likely related to the rapid decline and weakening of the Indian Summer Monsoon on the millennium scale.In summary,this study concludes that the relative abundance of C_3/C_4 plant and the long-term vegetation evolution in Yunnan China were mainly driven by the variation in regional precipitation,which is controlled by the Indian Summer Monsoon since the LGM.