Disentangling seasonal vegetation effects on ecosystem evapotranspiration and water use efficiency of Mediterranean savannah-type oak forest

由于生态系统水碳通量之间的紧密耦合，水是驱动生态系统生产力的关键因素之一。要了解水和碳通量的发展，特别是在水有限的生态系统中，全球气候变化预计会加剧干旱并改变降水模式，就需要对蒸散和光合作用有功能性的了解。该项目的目的是一个详细的机械评估的水平衡和水利用效率的一个典型的地中海稀树草原栎林。该项目将侧重于这一两个组成部分的系统的地上和地下植被的季节动态，以及植被对水和碳通量的反馈。该研究将结合联合收割机（1）生态系统和林下净CO2和H2O通量的测量，（2）一种实验方法（挖沟样地设计），以解开主要植被对水和碳过程的影响，（3）一种建模方法，以整合从不同尺度获得的信息。通过使用稳定同位素，将净水通量划分为各个组成部分。该项目将提供对生态系统水循环和水利用效率的基于过程的理解，特别关注林下植被的贡献，并将在考虑未来气候趋势的情况下对其进行评估。这种更好的了解将有助于制定适当的管理战略，也是评估气候变化对地中海生态系统影响的风险所必需的。

Water represents one of the key factors driving ecosystem productivity due to the tight coupling between ecosystem water and carbon fluxes. A functional understanding of evapotranspiration and photosynthesis is required to understand the development of water and carbon fluxes, particularly in water-limited ecosystems where global climate change is expected to intensify drought and alter precipitation patterns. The aim of this project is a detailed mechanistic evaluation of the water balance and water use efficiency of a typical Mediterranean savannahtype oak woodland. The project will focus on seasonal dynamics of over- and understorey vegetation of this two-component system and on the vegetation feedbacks on water and carbon fluxes. The study will combine (1) ecosystem and understorey measurements of net CO2 and H2O fluxes with (2) an experimental approach (trenching plot design) to disentangle major vegetation effects on water and carbon processes, and (3) a modelling approach to integrate the information gained from the different scales. Partitioning of net water fluxes into their individual components will be achieved by the use of stable isotopes. This project will deliver a process-based understanding of ecosystem water cycling and water use efficiency with a particular focus on the contribution of the understorey, which will be evaluated under consideration of future climate trends. Such improved understanding will help to develop appropriate management strategies and is needed for a risk assessment of climate change impact on Mediterranean ecosystems.