风成红土碳同位素组成与新近纪植被演化

The origin and expansions of C4 plants are among the most prominent ecological changes in the Cenozoic Era. Contentions still persist with regards to the timing of their appearance, the evolution history and the underlying causes. Based on the newly recovered Neogene loess-soil sequence in northern China containing more than 400 paleosols, this project aims at (1) reconstructing the history of C3/C4 biomass in the past 22 Ma in northern China through analyzing the carbon isotope of pedogenic carbonate, bulk organic matter and long-chain n-alkanes; (2) characterizing the properties of the paleosols and the changes of pollen assemblages to provide additional constraints to the isotopic interpretations; (3) depicting the roles of temperature, precipitation, seasonality and CO2 concentration changes on the C3/C4 biomass using an Inversed Vegetation Model (IVM), and (4) addressing the links of the C4 plant history with the Neogene-Quaternary geological and environmental changes of global significance, including the global cooling, changes of the Asian monsoon and inland aridity, as well as the uplift of Tibetan Plateau. The results are also expected to provide new insights for evaluating the impacts of the upcoming global warming and CO2 increase on the ecosystem.

C4植物的起源和扩张是新生代具全球意义的生态事件之一。然而，学术界对其起源时代、演化历史和成因仍有诸多争议。本项目以我国北方新近纪基本连续的、具高质量年代控制的风成红土序列及其中的400余层古土壤为主要研究对象，通过成壤碳酸盐、有机质和长链正构烷烃的碳同位素分析、古土壤学和孢粉学研究，结合最新的植被反演数值模拟方法，重建22 Ma以来我国北方C4植物的演化历史，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，揭示植被演化与新生代全球变冷过程、青藏高原隆升、东亚季风演化和亚洲内陆干旱化等重大地质-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我国北方C3/C4生物量的变化趋势提供自然背景参考。

C4植物的起源和扩张是新生代具全球意义的生态事件之一。到目前，学术界对其起源时代、演化历史和成因仍有诸多争议。项目以我国北方新近纪基本连续的、具高质量年代控制的风成红土序列及其中的400余层古土壤为主要研究对象，通过成壤碳酸盐、有机质和长链正构烷烃的碳同位素分析、孢粉学和数据集成研究，重建了我国黄土高原晚新生代以来C3、C4植物的演化历史，揭示出C4植物在早中新世就已广泛存在，是全球最早的起源地之一，之后C4植物丰度逐步降低。结合新数据和植被反演数值模拟方法，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，揭示出中新世以来C4植物逐步降低受全球温度变化的强烈影响、尤其与夏季温度降低有关；降水和CO2浓度变化对轨道尺度的C3、C4植被变化有显著影响；三个要素的组合变化共同控制了我国北方C3/C4植物的演化历史。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。