东北典型植物群落的表土植硅体记录及晚冰期以来的古植被定量重建

Located at the northern edge of East Asian monsoon area, Northeastern China is very sensitive to past global changes. Abundant records suggest that significant climatic fluctuations and vegetation succession have taken place in NE China during the Quaternary. Thus, reconstructing the paleo-vegetation in NE China is essential for our understanding of vegetation dynamics in East Asia and its responses to climate change. In addition, this may also provide proper guidance in the area of biodiversity conservation, rational utilization of resources and ecological early-warning, and so on. In this project, phytolith assemblages both in plants and topsoil of several selected plant communities and characteristic parameters of these communities (e.g. richness, coverage) are investigated. And then we target to explore the differences in source and preservation degree of different phytolith types among these selected plant communities in NE China. After this, employing discriminant analysis and rarefaction analysis, we will build a quantitative relationship between the phytolith assemblages (in topsoil) and characteristic parameters of a given plant community. Therefore we can use phytolith assemblages in topsoil to identify different plant communities directly. Then the quantitative relationship will be applied to several profiles in NE China. Based on high-accuracy AMS 14C dating results, we intend to reconstruct the paleo-vegetation dynamics in NE China since the late-glacial time precisely and panoramically. In addition, pollen analysis is adopted to verify the accuracy of phytolith-based paleo-vegetation reconstruction. Finally, we will achieve a more accurate temporal-spatial pattern of paleo-vegetation in NE China at some important time windows since the late-glacial period.

东北地区处于东亚季风区北部，对过去全球变化十分敏感。重建该区第四纪以来的植被变迁对于了解欧亚大陆东缘的植被动态及其对气候变化的响应具有重要意义，也将有利于正确指导该区生物多样性保护、资源合理开发利用及生态预警等。本项目以植硅体分析为主要研究手段，辅以孢粉分析，通过系统开展典型植物群落下表土植硅体的来源及其保存的差异性研究，明确表土植硅体组合对上覆植物群落的代表性，探寻表土植硅体与上覆群落数量特征间的定量关系。进而建立适合本区不同植物群落判别的表土植硅体标准，通过引入稀疏分析等数学模型，进一步刻画古植物群落的植物组成与数量特征。结合AMS14C定年结果，将上述判别标准应用于若干沉积剖面中，以达到高精度、全景式地重建东北地区晚冰期以来古植被动态之目的，并通过与该区“孢粉—古植被”重建结果进行对比验证，从而更加准确地探讨研究区内晚冰期以来典型时段的古植被面貌。

中国东北地区位于欧亚大陆与太平洋的过渡地区，深受东亚季风的影响，为全球环境变化的一级敏感带，生态环境脆弱而敏感，是开展全球变化研究的理想区域。基于植硅体重建东北地区晚冰期以来古植被动态，对于了解欧亚大陆东缘气候和植被的演化过程及生物多样性保护具有重要的科学意义。项目组依据项目实施方案，在东北地区共布设了213个采样点，采集植物单种77种，调查和采集群落样品466个，同时，采集表土样品607个，钻取沉积剖面13个。此外，项目组还对采集的5个连续沉积的泥炭剖面进行了高分辨率采样，共获得了约1300余个沉积剖面样品。.项目组在对剖面和表土样品提取植硅体和孢粉数据的基础上，使用多种数理统计分析手段，对实验结果进行深入分析讨论，取得了丰富的理论成果。首先，项目组通过研究东北地区植物单种以及群落的植硅体组合特征，定量刻化了木本和草本植硅体的形态差异，建立二者的识别标准，并应用主成分分析和判别分析实现了表土样品对上覆植物群落的判别。其次，项目组引入了代表性指数，包括联合指数(A)、超代表性指数(O)和低代表性指数(U)，相似系数(CC)和相关系数(C)以定量评估东北地区表土植硅体的代表性。最后，在探究晚冰期以来东北地区古植被历史方面，为了高精度、全景式地重建该地区晚冰期以来古植被动态变迁历史，项目组完成了四个泥炭剖面及一个风沙古土壤剖面的植硅体、孢粉分析工作，在得到各泥炭剖面植硅体、孢粉组合特征的基础上，结合现代植硅体的植被判别函数及 W/G 指数值域，分别确定了五个剖面不同时间段的植被类型，并定量解译剖面植硅体所指示的植被覆盖程度及面貌特征。