热带望天树季节雨林木本植物的水分关系及对极端干旱的响应

望天树（Parashorea chinensis）是我国特有的一级珍稀濒危物种，也是我国热带雨林的旗舰树种，具有极高的保护和生态学价值。最近几十年来其所在分布区干旱不断加剧，极端干旱事件频发，尤其是2019年以来极端干旱可能正对望天树及所在的低地热带季节雨林产生不可逆的影响。然而，当前学术界对于望天树热带雨林的水分关系、对其干旱响应策略以及生理学机制鲜有报道。本项目拟选择热带北缘以望天树为建群种的热带季节雨林生态系统为研究对象，依托林冠塔吊和森林动态监测样地，结合水力学性状和解剖特征测定、野外生理生化及生长过程的长期监测、群落学调查、生态系统控制实验和模型模拟，探讨极端干旱对望天树带季节雨林的代表性物种的影响及作用的生理生态学机制，并且在此基础上建立干旱对热带季节雨林生态系统群落结构影响的机理模型，为进一步预测当前频发的极端干旱事件对望天树热带季节雨林生态系统群落动态提供理论依据。

Parashorea chinensis H. Wang (Dipterocarpaceae), the flagship species of lowland tropical rainforests, is a rare and endangered species in China with extremely high conservation and ecological values. P. chinensis rainforests mainly distribute along the stream where typically have high soil water availabilities hence are believed to be susceptible to water stress. However, there is a clear trend of increasing frequency and intensity of drought in southwest China (especially in Xishuangbanna) due to strong El Nino effects in the past decades, which may be exerting irreversible effects on the composition and dynamics of the tropical rainforests. For instance, the extreme drought event associated with heat wave since 2019 until now resulting in a vast canopy dieback and tree mortality in the whole region of Xishuangbanna. Meanwhile, we are still unclear how and what extent of these lowland P. chinensis rainforests are being affected by the current prolonged drought event thus hinder the prediction and modeling of their response to the future climate change scenarios. In this project, with the help of an 88-m-high forest canopy crane, we will investigate a combination of drought-related functional traits for the common species in P. chinensis rainforests, together with the in situ monitoring of the seasonal dynamics in xylem water status, xylem embolism, sap flow, the (non-structural carbohydrate) NSC pool in different organs, the stem radial growth both in a natural condition and in rainfall exclusion treatment (30% and 60% rainfall exclusion) experiment over years to manipulate the different future drought scenarios. Our trait data will be tested on their reliability and performance in the prediction on drought-induced mortality based on the census record in a neighboring 20-ha CTFS permanent plot. The main objectives are:(1) to understand how and to what extent the common species in P. chinensis rainforest are being affected under modest and extreme drought? (2) characterize the capacity of forest trees to withstand and acclimate to drier conditions? (3) explore the hydraulic safety margins of forest trees to the current extreme drought. Because drought severity and frequency are projected to increase with temperature-driven rises in evaporative demand in this century, our findings will help us to predict the drought impacts on the P. chinensis rainforests and forecast the potential response of P. chinensis rainforests to future droughts under future climate change scenarios.