中国西南季风区末次冰盛期以来C3/C4植物时空格局及对气候变化的响应

Increases in global atmospheric pCO2 and temperature in the future may result in significant changes in monsoon circulation, ecological environment and agricultural production pattern. In order to evaluating the consequences, one important approach is to analyze the “similar model” happened in geological history, namely reconstruction of relative abundance of C3 and C4 vegetation from the Last Glacial Maximum to Holocene Thermal Maximum both in historical and spatial distribution. Southwest China is an important area for food crop production and C3 and C4 vegetation development, which is strongly under the influence of southwest summer monsoon. However, researches on evolution history of C3 and C4 vegetation in southwest China remain sparse, and the corresponding relationship with climatic and environmental conditions is still patchy. Based on AMS 14C and 210Pb dating, through comprehensive analyses of geophysical and geochemical characteristics, biomarkers as well as compound-specific carbon isotope compositions of long-chain n-alkanes of typical lake sediments in southwest China, therefore, our research aims to reconstruct the C3 and C4 vegetation distribution pattern and evolution history, and to determine the corresponding relationship between the evolutions of C3 and C4 vegetation and the variations of paleoclimate and paleoenvironment as well as the main driving factor. These results may provide scientific information for predicting future vegetation changes and agricultural patterns in response to on-going global warming.

未来全球大气CO2浓度和平均温度增加，将会对我国季风环流、生态环境和农业生产格局产生深刻影响。通过研究地质历史时期“相似型”，即重建末次冰盛期到全新世大暖期C3/C4植被生物量时空格局可为评估此影响提供科学参照。我国西南地区是粮食作物和C3/C4植物混合分布区，气候环境条件受到西南季风深刻影响。然而，该地区有关C3/C4植被演化的研究工作尚未系统展开，植被演替历史及对气候环境的响应关系尚不清楚。本项目拟以我国西南季风区典型湖泊沉积物为研究对象，在AMS 14C和210Pb测年基础上，通过沉积物地球物理和地球化学指标、生物标志化合物以及正构烷烃单体碳同位素组成的研究，重建研究区末次冰盛期以来的C3/C4植被生物量时空格局和演化历史，探讨C3/C4植被演化对气候环境特征的响应及其主要驱动因素，为评估未来气候变暖对我国西南地区植被分布和农业生产的影响提供科学依据。

全球气候变暖将会对我国季风环流、生态环境和农业生产格局产生深刻影响。然而，目前我国西南季风区C3/C4植被演化时空格局及其对气候环境的响应关系尚不清楚。利用地质历史“相似型”，重建末次冰盛期到全新世大暖期C3/C4植物生物量演化历史可为评估全球变暖对生态环境和农业生产的影响提供科学参照。本项目以我国西南季风区邛海湖泊钻孔沉积物为研究对象，基于AMS 14C年代学框架，利用多指标综合体系（沉积物粒度、磁化率、烧失量、TOC和TN、有机碳同位素、正构烷烃、正烷基-2-酮、GDGTs、主微量元素以及正构烷烃单体碳同位素）重建了西南季风区过去27.7 cal ka BP以来的气候环境演化历史和C3/C4植被时空演化格局，重点捕获了LGM、H1、YD、HCO等典型冷暖气候事件；定量重建了过去27.7 cal ka BP以来的古温度序列，明确了LGM时期温度比现今低3 oC，HCO时期温度比现今高2.5 oC，基于brGDGTs重建的MAT和指示湿度和降水变化的pH指标和沉积物粒度特征，进一步确认西南季风区温度和降水协同演化，呈现雨热同期的特征；基于C4植物生物量演化特征，揭示了温度和季风降水是影响西南季风区C4植物生长的主要因素，同时提出在季风降水不变的情况下，推测在本世纪末全球平均增温2 oC的背景下，西南季风区C4植物生物量将增加~10%。研究结果为评估未来全球气候变暖对西南季风区植被分布和农业生产格局的影响提供了重要理论依据。

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