Assessing dynamics in eco-hydrological processes during drought stress across scales in a grassland community by stable isotopes

气候变化情景所预测的干旱期延长等水文极端事件会影响陆地植物生态、群落结构和抵抗力，特别是在草原等浅根群落。然而，植物群落结构变化和潜在的机制生态水文响应（即，水的使用、碳的吸收）对草原群落的影响在很大程度上仍然不清楚，也很难观察。在不同的尺度上（从单个植物到植物群落），涉及到许多过程，生态水文过程的动态之间存在着强烈的反馈。例如，植物蒸腾作用由土壤水的可用性和大气需求驱动的光合作用期间通过气孔的蒸腾水分损失（叶-空气水蒸气赤字）控制。此外，利用各种土壤水库的能力和气孔控制水分流失的敏感性是种特异性的。在这方面，稳定的H2O和CO2的同位素组成的过程发生在土壤-植被-大气连续体的有见地的指标，特别是因为新的技术发展，现在可以近连续observations.The项目的目的是详细的机制分析的植被生态水文响应延长干旱期使用H2O和CO2通量和同位素测量。这将与社区对结构和生物量生产的反应相联系。我们将在三个相互作用的工作包（WP）中研究从工厂到社区水平的这些方面。WP 1的重点是根吸水（RWU）的反应，以延长干旱的单株植物，以及观察植物-植物相互作用的平衡在受控的实验室条件下的变化。WP 2将RWU配置文件中的响应和H2O和CO2的净生态系统通量（分为蒸腾和蒸发以及总碳吸收和呼吸）与群落结构响应联系起来。将在纳入国际干旱控制网络的实地条件下进行一项为期两年的降水控制试验。在WP 3中，实验室获得的数据将用于校准详细的三维土壤-根系模型R-SWMS。这将为一维土壤-植被-大气传输模型SiSPAT-Isotope提供放大的根生长、RWU和蒸腾模块。然后，利用SiSPAT-同位素进行的模拟将与实地获得的数据进行对比，以估计干旱期的水文响应。这将提供一个过程为基础的了解生态水文土壤植被大气反馈，以应对长期干旱期，这将有助于发展的可持续性预测气候变化对草原社区的影响。

Hydrological extreme events as extended drought periods predicted by climate change scenarios impact terrestrial plant ecology, community structure and resistance, particularly in shallow rooted communities such as grasslands. However, the interplay between structural changes in plant communities and the underlying mechanistic ecohydrological responses (i.e., water-use, carbon uptake) of grassland communities to drought spells remain largely unclear and are hard to observe. At distinct scales (from single plants to the plant community) a multitude of processes are involved and strong feedbacks exist between the dynamics of ecohydrological processes. Plant transpiration, for example, is controlled by the availability of soil water and transpirational water loss through stomates during photosynthesis driven by the atmospheric demand (leaf-to-air water vapour deficit). Moreover, the capacity to utilize various soil water pools and sensitivity of stomatal control of water loss is species-specific. In this regard, stable isotope compositions of H2O and CO2 are insightful indicators of processes occurring in the soil-vegetation-atmosphere continuum, specifically since new technical developments now enable near continuous observations.The aim of this project is the detailed mechanistic analysis of the vegetation eco-hydrological response to extended drought periods using H2O and CO2 flux and isotopic measurements. This will be linked to community responses regarding structure and biomass production. We will study these aspects from the plant to community level in three interacting work packages (WP). WP1 focuses on root-water uptake (RWU) response to extended drought of single plants as well as observing shifts in the plant-plant interaction balance under controlled laboratory conditions. WP2 will link responses in RWU profiles and net ecosystem fluxes of H2O and CO2 (partitioned into transpiration and evaporation and gross carbon uptake and respiration) to community structural responses. A two years precipitation manipulation experiment will be conducted under field conditions integrated in an international drought manipulation network. In WP3, data acquired in the laboratory will be used to calibrate the detailed three-dimensional soil-root model R-SWMS. This will provide up-scaled root-growth, RWU and transpiration modules for the one-dimensional soil-vegetation-atmosphere transfer model SiSPAT-Isotope. Simulations with SiSPAT-Isotope will then be confronted to data acquired in the field for estimation of the hydrological response to drought periods. This will deliver a process-based understanding of the eco-hydrological soil-vegetation-atmosphere feedbacks in response to extended drought periods, which will help in the development of sustainability predictions of the climate change impacts on grassland communities.