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

由于生态系统水通量和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，特别是在预计全球气候变化将加剧干旱和改变降水模式的水资源有限的生态系统中，需要对蒸发蒸腾和光合作用的功能有一个了解。该项目的目的是对典型的地中海稀树草原型橡树林地的水平衡和水利用效率进行详细的机制评估。该项目将重点关注这一双组分系统中上层和下层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(1)生态系统和林下二氧化碳和水的净通量测量；(2)实验方法（沟槽样地设计）来解开主要植被对水和碳过程的影响；(3)建模方法来整合从不同尺度获得的信息。通过使用稳定同位素，可以将净水通量划分为各自的组成部分。该项目将提供基于过程的生态系统水循环和水利用效率的理解，特别关注下层植被的贡献，将在考虑未来气候趋势的情况下进行评估。这种更好的理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需要的。

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.