南亚孟加拉盆地C4植物扩张历史及其成因研究

The expansion of plants characterized by the C4 photosynthetic pathway during the late Tertiary was a major paleoecological event in Earth’s terrestrial history. To date, the contentious issue still persists with the evolution history and its underlying causes. Based on the newly recovered Neogene sequence in Bengal basin of Sothern Asia, this project aims at (1) dating the sedimentary sequence using high-precision magnetostratigraphic study; (2) reconstructing the history of C3/C4 biomass since the Neogene in Bengal basin on the basis of analyzing the carbon isotope of long-chain n-alkanes, and characterizing the properties of pollen assemblages to provide additional constraints to the isotopic interpretations; (3) depicting the roles of seasonal temperature, precipitation and CO2 concentration changes on the C3/C4 biomass using an Inversed Vegetation Model (IVM), and (4) addressing the links of the C4 plant expansion history with the evolution of Indian monsoon, the uplift of Tibetan Plateau, and the global cooling. These results are also expected to provide new insights for evaluating the impacts of the global warming and CO2 increase on the C3/C4 ecosystem in the future.

C4植物的扩张是新生代具全球意义的生态事件之一。到目前为止，学术界对其演化历史和成因仍有重大争议。本项目以南亚孟加拉盆地新近纪沉积为主要研究对象，通过高精度的磁性地层研究，建立高质量的年代序列；利用有机质长链正构烷烃的碳同位素分析和孢粉学研究，结合最新的植被反演数值模拟方法，重建新近纪以来南亚孟加拉盆地C4植物扩张和季风演化历史，解析气候要素(温度、降水及季节特征)和CO2浓度变化对C4植物演化的影响，揭示植被演化与南亚季风演化、青藏高原隆升和新生代全球变冷等重大地质-环境事件的联系，并为理解未来CO2浓度升高和全球增温背景下南亚C3/C4生物量的变化趋势提供自然演化的参考。

C4植物的扩张是新生代具全球意义的生态事件之一。到目前为止，学术界对其演化历史和成因仍有重大争议。本项目以南亚孟加拉盆地新近纪沉积为主要研究对象，结合东亚黄土高原风成沉积序列，利用成壤碳酸盐和有机质碳同位素分析、孢粉学研究以及新的植被反演模拟方法，重建新近纪以来亚洲C4植物扩张演化历史。南亚热带C4植物在~7Ma呈现大幅度的扩张，而东亚温带黄土高原直至~4Ma才出现较明显的扩张，具有显著的区域差异；亚洲C4植物的扩张，主要受控于夏季降水减少，CO2浓度变化对其影响处于次一级，揭示出C4植物扩张与不同时段南亚和东亚夏季风的减弱有关，并非原先所认为有亚洲季风的增强，上述C4植物演化可能与低纬热带海洋变化有关。研究了我国C3、C4植物时空演化格局及未来变化趋势，揭示出轨道尺度上C4植物变化呈现明显的南北反向特征，冰消期以来北方区域C4植物丰度的增加主控于温度升高，而南方区域C4丰度的降低是CO2浓度和降水量增加共同作用的结果。在未来增温情形下，我国北方C4植物丰度可能将明显增加，而南方区域则减少。