Radial Water Exchange Between Roots and Soil

9419841诺贝尔拟议研究的主要目标是研究水分通过根-土壤界面以及从根表面到根木质部的运动。重点将放在路径的每个组成部分中对径向流动的约束如何随着土壤水分有效性的变化而变化。将分析干旱和随后的复湿期间根和根-土壤界面的结构变化对单子叶龙舌兰和双子叶仙人掌根系吸水或失水的影响。穿过根的途径由几个组织组成，每个组织都有自己的水力传导性，可以随着水分的可获得性和根的发育而改变。将通过测量完整和解剖的根段的水力传导性来研究单个根组织对径向水流的限制；质外体对径向途径的贡献也将通过荧光示踪剂进行评估。将评估在短期干旱(不到一个月)期间在根中发生的解剖变化以及组织渗透压的可能变化；将根据流体静压和渗透压这两个驱动力来分析限制水流动的这种变化的重要性。还将研究根对长期干旱(4至6个月)的反应，重点是限制水分损失但允许在重新湿润时快速吸收水分的解剖和形态变化。这些物种和许多其他物种的根在干旱时会收缩，土壤可能也会收缩，导致根和土壤之间形成气隙。对根部周围气隙的物理验证和测量将从根部周围的土壤薄片中获得，同时还将通过实验评估气隙对穿过根-土壤界面的水分运动的影响。总之，拟议的研究将调查根-土壤系统中水分运动的限制如何随着土壤水分的可获得性而变化，重点是根在干燥土壤中发挥作用的能力。

9419841 Nobel The primary goals of the proposed research are to investigate water movement across the root-soil interface and from the root surface to the root xylem. The focus will be on how the constraints on radial flow in each component of the pathway change in concert with changes in soil moisture availability. Structural modifications in the root and at the root-soil interface during drought and subsequent rewetting will be analyzed with respect to their consequences for water uptake or loss by roots of the monocotyledon Agave deserti and the dicotyledon Opuntia ficus-indica. The pathway across the root is composed of several tissues, each with its own hydraulic conductivity that can change in response to moisture availability and as a consequence of root development. The limitations on radial water flow imposed by individual root tissues will be investigated by measuring hydraulic conductivity for intact and dissected root segments; the contribution of the apoplast to the radial pathway will also be assessed by fluorescent tracers. Anatomical changes that occur in roots during short-term drought (less than one month) will be assessed along with possible changes in tissue osmotic pressure; the importance of such changes in limiting water flow will be anlyzed with respect to two driving forces, hydrostatic versus osmotic pressures. The responses of roots to prolonged drought (four to six months) will also be examined, with the focus on anatomical and morphological changes that restrict water loss yet allow rapid water uptake upon rewetting. Roots of these and many other species shrink during drought, as perhaps does the soil, leading to the development of air gaps between roots and soil. Physical verification and measurement of air gaps around roots will be obtained from soil thin-sections surrounding roots, accompaied by experimental assesment of the effects of air gaps on water movement across the root- soil interface. In summary, the proposed research will investigate how the limitations on the movement of water in the root-soil system change with soil moisture availability, with particular emphasis on the capability of roots to function in drying soil.