Using advances in stable water isotopy to quantify species- and interspecific ecohydrological feedback processes and water transit times of different tree stands

据预测，未来水文极端事件的发生率和严重程度将发生重大变化。理解降水输入、土壤和地下水中的水储存以及集水区输出水通量之间的复杂联系和相互作用仍然是生态水文学的一个重大挑战。植被在水文循环中起着举足轻重的作用，控制着50- 70%的陆地蒸散量.不同的植物物种在它们的水分利用策略上有很大的不同。整合这些信息物种特定的土壤渗透，水力再分配和根水分吸收动态变化提供了第一个提示，树木如何可能漏斗水对他们的活跃的根区。这将成为重要的在未来的气候条件下，可持续森林生态系统管理的适应战略的发展。水年龄的概念，通过水同位素被用来评估如何不同的流动路径有助于径流，以及这些贡献如何随时间变化。水年龄提供了一个不同的层面，除了水文响应，有助于更好地了解水文过程，提高水文模型的现实性。这一概念主要用于关注（生态）水文循环或整个流域的各个分区。然而，最近在渡越时间估计方面的发展表明，我们需要考虑隔室之间的界面（例如，土壤-大气或土壤-根系），以便更全面地了解生态水文循环。因此，物种的具体差异和互补资源利用的树木在混交林可能会改变水的过境时间和年龄在ecohydrogencycle. We的中心假设是，物种的身份和树种之间的水分竞争是一个主要的驱动程序，生态水文土壤-树木反馈过程。我们将研究我们的中心假设在一个综合实验（工作包（WP）1-3）和建模方法（WP 4），其中高空间分辨率的同位素，水文，经典和新颖的植物生态生理测量将结合连续的长期监测，以量化生态系统的水循环的所有隔间的纯和混合的立场冷杉和山毛榉树。将通过一个新的原位同位素监测平台（SWIP）为期一年（WP 1）观察自然丰度水平上的水通量和水池的同位素特征，以验证SWIP系统对特定树种和土壤类型的影响。在WP 2中，我们将进行同位素标记实验，以量化特定的时间异质性的生态系统隔间的响应时间。WP 3将侧重于解开不同生态系统隔间的过境时间和水年龄。在WP 4中，我们将使用SWIS将所获得的数据应用于生态水文过程模型。我们将改进和调整模型结构，以适应不同的树木。

Significant changes in hydrological extreme events are predicted to increase in occurrence and severity in the future. Understanding the complex linkages and interactions between precipitation inputs, water storage in the soil and groundwater, as well as catchment output water fluxes is still a major challenge in ecohydrology. Vegetation plays a pivotal role in the hydrological cycle controlling 50-70 % of terrestrial evapotranspiration. Distinct plant species differ significantly in their water use strategies. Integrating such information on species-specific alterations of soil infiltration, hydraulic redistribution, and root-water uptake dynamics delivers first hints on how trees may funnel water towards their active root zones. This will become important under future climatic conditions and the development of adaptation strategies for a sustainable forest ecosystem management.The concept of water ages by means of water isotopes is used to assess how different flow paths contribute to runoff and how these contributions change over time. Water ages provide a different dimension in addition to hydrometric responses, helping to better understand the hydrological processes and improve the realism of hydrological models. This concept mostly has been used to focus on individual compartments of the (eco-)hydrological cycle or the whole catchment. However, recent developments in transit time estimations, demonstrate that we need to consider the interfaces among the compartments (e.g., soil-atmosphere or soil-roots) for a more holistic understanding of the ecohydrological cycle. Therefore, species-specific differences and complementary resource utilization of trees in mixed stands might alter water transit times and ages in the ecohydrological cycle.Our central hypothesis is that species identity and water competition between tree species is a major driver for ecohydrological soil-tree feedback processes. We will investigate our central hypothesis on pure and mixed stands of fir and beech trees in a combined experimental (work packages (WPs) 1-3) and modelling approach (WP 4), where high spatial resolution of isotopic, hydrometric, classical and novel plant eco-physiological measurements will be combined with continuous long-term monitoring to quantify all compartments of the ecosystem’s water cycle. Isotopic signatures of water fluxes and pools on a natural abundance level will be observed via a novel in-situ isotope monitoring platform (SWIP) for one year (WP 1) to validate the SWIP system for the specific tree species and soil types. In WP 2, we will conduct an isotope labelling experiment to quantify stand specific temporal heterogeneity of the ecosystem compartment’s response times. WP 3 will focus on unravelling transit times and water ages of the distinct ecosystem compartments. In WP 4, we will apply the acquired data to model ecohydrological processes using SWIS. We will improve and adapt the model structure to the different tree stands.