青藏高原大气孢粉传输、分布格局及其环境意义研究

Modern pollen distribution and its relationship with vegetation and climate are fundamental for vegetation and climate reconstruction using sediment pollen records. On the Tibetan Plateau (TP), the third pole, modern pollen researches have been focused on quantitative relationship between pollen and climate, however, pollen source and transportation process on large scale have been poorly investigated so far. Airborne pollen, as biological particles in the air reflecting vegetation response to climate changes, is a potential key to deepen the modern pollen research on the TP. In this project, airborne pollen research will be conducted systematically. Using Cour pollen traps, airborne pollen sampling spots will be set up across the TP and surrounding areas, including the westerly domain, monsoon domain and transitional domain to continuously collect the airborne pollen. The spatial and temporal distribution patterns of airborne pollen in the TP will be achieved and as well as their relationships with climate, atmospheric circulation, elevation, vegetation distribution, plant phenology, etc. To be compared with surface soil and lake surface sediment pollen samples, with the support of different kinds of source simulation models, major airborne pollen sources and transportation routines and their impacts and dynamics will be clarified. Thus, the results could supply new evidences and cognitions to understand the past climate changes under different atmospheric circulations and vegetation response to global change in the Tibetan Plateau.

现代孢粉分布及其与植被、气候关系的研究是利用孢粉分析重建古环境的基础。青藏高原现代孢粉过程研究主要集中在孢粉与植被、气候的统计关系上，而孢粉来源、传播等关键环节仍缺少深入的研究，大气孢粉是深入研究孢粉现代过程的重要介质。本项目拟在青藏高原系统地开展大范围大气孢粉研究，利用风标花粉仪在西风/季风控制区及其过渡区收集大气孢粉样品，认识大气孢粉组合的时空分布特征及其与气候条件、西风/季风环流、植物物候、植被分布、海拔高度等的关系；通过大气孢粉与表土/表层沉积物孢粉样品的对比，结合源区模拟模型分析大气孢粉来源与传输途径及其影响因素和动力，探讨大气孢粉所反映的大气环流信息、植被和气候信息及其在沉积物中的保存程度，从而为研究历史时期不同大气环流影响下的青藏高原气候变化与植被响应提供科学基础。

现代花粉分布及其与植被、气候关系的研究是利用花粉分析重建古环境的基础。青藏高原现代花粉过程研究多集中于表土或湖泊表层沉积物。由于表土或表层沉积物花粉是一个时期沉积的结果，难以反映花粉物候及其代表的植被状况；但从现代大气花粉的视角出发，分析大气花粉组合及其与气候、植被、大气环流的关系，能够深入认识沉积花粉组合反映的物源及其大气环流条件。本项目在青藏高原南部季风区和中部西风/季风过渡区系统收集大气花粉样品，发现不同区域的大气花粉组合能够反映区域的植被和气候特征。不同类型的花粉对气候因子的响应不同，草本花粉对气温、降水更敏感，乔、灌木花粉与风向、风速关系更密切。大气花粉组合和数量具有明显的季节变化，季风期（6-8月）花粉浓度高且以草本为主，西风期（9-5月）花粉浓度很低且以外来的乔木花粉为主。不同季节的花粉组合特征可以作为大气环流的判别指标。大气花粉的年际和季节变化受植物物候、气温、降水等影响。乔木/非乔木花粉比值（AP/NAP）可以作为指示青藏高原半干旱无林区气候和植被变化的指标，AP/NAP比值越高，指示西风为主、冷干环境下的稀疏植被特征。大气花粉作为大气生物和气候事件的载体，对其进行长期观测研究，将为理解植被响应气候变化以及沉积物花粉记录的环境解释提供参考。