Collaborative Research: Determining the role of hydraulic redistribution regimes in the critical zone - an experimental and modeling synthesis

理解和预测地上和地下生态水文过程之间的相互作用是具有挑战性的。根在连接地上植物与大气的碳、水和能量交换等生理生态过程，以及与土壤水分和碳、微生物和养分动态相关的地下过程中起着重要作用。有趣的是，根系水分运动并不总是单向的;植物通过一种称为“水力再分配”的现象为优先水分运动创造了途径，通过这种现象，水分在潮湿时期通过根系向下移动，但在干燥时期向上移动。本项目将研究这种水力再分配。这项研究将为旱地地区提供深入的见解，并使人们能够更广泛地概括地下水、根系和地上生物群之间的相互作用及其在整个生态系统绩效中的作用。本研究的突出方面是实地研究和建模之间的耦合，使假设检验，并提供了一个基于站点的研究升级框架。鉴于气候变暖的预测，人们对生态系统如何应对长期压力的科学兴趣迅速扩大。该项目的科学目标是系统地研究根系水力再分配的作用，作为促进地上-地下联系的机制，推动水和碳的动态变化，并形成土壤水分和植被分布的紧急空间格局。将在亚利桑那州南部的两个地点开展实地活动：一个是利用地下水源增加降水量的河岸地点，另一个是缺乏这种二级水池的高地地点。本研究将推进理解地上和地下生态水文过程的相互作用的理论，使用一个模型，机械地解决相关过程。根和茎汁液通量、土壤、碳、整株植物和生态系统尺度（通过涡度协方差塔）的耦合建模和田间试验和监测将相互通报，以提供一系列尺度的详细见解。这项研究的结果将在生物圈2号旅游路线上的信息亭中展示，每年有超过10万名游客，其中包括K-12学生和退休人员。

Understanding and predicting interactions between aboveground and belowground ecohydrologic processes is challenging. Roots play an important role in linking aboveground plant ecophysiological processes, such as carbon, water, and energy exchange with the atmosphere, and the belowground processes associated with soil moisture and carbon, and microbial and nutrient dynamics. Interestingly, root water movement is not always unidirectional; plants create pathways for preferential water movement through a phenomenon called "hydraulic redistribution", by which water moves downward through the roots during wet periods but upward during drier periods. This project will study such hydraulic redistribution. The study will both provide insights for dryland regions and enable broader generalizations regarding the interaction between groundwater, roots, and aboveground assemblages and their role in whole-ecosystem performance. The salient aspect of this study is the coupling between field research and modeling to enable hypotheses testing and provide an upscaling framework from site-based studies. Given projections of a warmer climate, there has been a rapid expansion in scientific interest in how ecosystems will respond to periods of prolonged stress. This research will help address this critical issue.The scientific objective of the project is to systematically examine the role of hydraulic redistribution by roots as a mechanism for facilitating aboveground-belowground linkages that drive water and carbon dynamics, and the development of emergent spatial patterns of soil moisture and vegetation distribution. Field-based activities will be conducted at two sites in southern Arizona: a riparian site where precipitation inputs are augmented with belowground water sources and an upland site that lacks this secondary water pool. This research will advance the theory for understanding the interaction of aboveground and belowground ecohydrological processes using a model that mechanistically resolves the related processes. Coupled modeling and field experimentation and monitoring of root and stem sap flux, soil, carbon, whole-plant, and ecosystem-scale (via eddy covariance tower) water and carbon fluxes will mutually inform each other to provide detailed insights at a range of scales. Results from this study will be presented in kiosks on the tour route of Biosphere 2 that sees over 100,000 visitors per year that include K-12 students to retirees.