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。根在连接地上植物的生态生理过程，如与大气的碳、水和能量交换，以及与土壤水分和碳有关的地下过程以及微生物和养分动态方面发挥着重要作用。有趣的是，根的水分运动并不总是单向的；植物通过一种被称为“水力再分配”的现象来创造优先水分运动的途径，即水分在潮湿时期通过根部向下移动，在干旱时期向上移动。本项目将对这种水力再分配进行研究。这项研究既将为旱地地区提供见解，也将使人们能够更广泛地概括地下水、根系和地上组合体之间的相互作用及其在整个生态系统性能中的作用。这项研究的突出方面是实地研究和建模之间的耦合，以支持假设检验，并提供一个基于现场研究的提升框架。鉴于气候变暖的预测，人们对生态系统将如何应对长期压力的科学兴趣迅速扩大。这项研究将有助于解决这一关键问题。该项目的科学目标是系统地研究根部水力再分配作为一种机制的作用，以促进驱动水和碳动态的地上-地下联系，以及土壤水分和植被分布的新兴空间格局的发展。将在亚利桑那州南部的两个地点开展实地活动：一个河岸地点利用地下水源增加降雨量，另一个地点则没有二级水池。这项研究将为理解地上和地下生态水文过程的相互作用提供理论基础，该模型可以机械地解决相关过程。对根和茎的汁液通量、土壤、碳、全植物和生态系统尺度(通过涡旋协方差塔)的水和碳通量的耦合建模和田间实验以及监测将相互影响，从而在一系列尺度上提供详细的见解。这项研究的结果将在生物圈2号旅游路线上的售货亭展示，生物圈2号每年接待超过10万名游客，其中包括从K-12学生到退休人员。

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.