末次冰盛期以来中国东北及邻区C4植物丰度的时空演化及其主控因素

SPATIOTEMPORAL CHANGES IN C_(4)PLANT ABUNDANCE AND THEIR DRIVING FACTORS IN THE NORTHEAST CHINA AND ADJACENT AREAS SINCE THE LAST GLACIAL MAXIMUM

C_(3)、C_(4)植物是陆地生态系统的重要组成部分,末次冰盛期(LGM,距今约2万年)以来全球大幅度增温,同时伴随大气CO_(2)浓度的不断变化。研究LGM以来C_(3)、C_(4)植物的时空分布及其驱动机制可为理解未来气候变暖背景下植物变化及应对未来陆地生态系统的挑战提供重要参考。中国东北地区位于高纬度季风边缘带,也是C_(3)、C_(4)植物混合区,其植被变化对气候响应敏感。对于东北地区C_(4)植物时空演化格局的研究还不完善。本研究基于9条湖泊、泥炭记录的长链正构烷烃单体δ13C和4条古土壤序列的土壤有机碳同位素(δ^(13)C_(SOM))记录,重建了LGM以来的东北及邻区C_(4)植物时空演化格局。结果表明,从LGM至全新世早期C_(4)植物丰度逐渐增加,在全新世早中期达到最高,平均可达约10%,之后再次下降。C_(4)植物丰度演化具有一定的区域差异,现今森林草原界线以东地区,其丰度在全新世早期(10~8 ka)达到峰值后下降;而以西的草原地区C_(4)丰度至LGM以来逐渐增加,全新世其丰度变化不大。在空间上,C_(4)植物丰度总体上呈现出由南向北递减的趋势,LGM时南北空间差异最小约为5%,而到全新世早期,其差异局部可达约20%。进一步将重建的C_(4)丰度演化与古气候记录对比,结果表明,末次冰盛期以来温度的升高可能是导致东北及邻区C_(4)植物扩张的主导因素。该项研究也进一步揭示,未来增温持续的背景下,东北地区C_(4)植物丰度可能增加,C_(4)植物分布的地理界限可能向更高纬扩张。

C_(3)and C_(4)plants are the fundamental part of the terrestrial ecosystem.The global climate system has experienced an overall warming trend since the Last Glacial Maximum(LGM)accompanied by constant changes in atmospheric CO_(2)concentration.Knowledge of the spatiotemporal pattern of C_(3)and C_(4)plants and their response to climate change since the LGM,is important for predicting the biosphere's response to future climatic warming.Here,the Northeast(NE)China and adjacent areas are located in the marginal zone of the region of influence of the East Asian summer monsoon(EASM),including Heilongjiang,Jilin,Liaoning provinces,and the northeast part of Inner Mongolia,with a mixed zone of C_(3)and C_(4)plants.It is therefore extremely sensitive to changes in climate.In this study,we reconstructed the spatiotemporal pattern of C_(4)plants in NE China and adjacent areas since the LGM,based on a synthesis ofδ^(13)C records of soil organic matter from 4 paleosol sequences andδ13C records of individual n-alkanes from 9 lake sediment sequences.The results indicate that the relative abundance of C_(4)plants increased after the LGM,reaching a maximum(average by about 10%)during Early-Middle Holocene,and then decreased.There was a difference in the temporal evolution of C_(4)plant abundance between the east and west parts of the boundary of forest and steppe.C_(4)plant abundance in the east parts indicated a decrease since the Holocene,while a relative stable change in west part during the Holocene.Spatially,the representation of C_(4)plants was characterized by increasing values from north to south.In addition,the smallest spatial difference(5%)in the representation of C_(4)plants between the north-west and south-east parts of NE China was during the LGM,and the largest spatial difference(20%)was during the Early Holocene.Comparing our results with the changes in climate and atmospheric CO_(2)concentration,the results suggest that increasing temperature was the dominant factor driving C_(4)plant expansion in NE China since the LGM.This may indicate the global warming would have benefited the development of C_(4)plant in NE China in future.