Capacitance Influences on the Water Relations of Desert Perennials

水是沙漠植物生长和存活的关键。它可以储存在嫩芽中，这对多肉植物特别明显，如龙舌兰(常见的沙漠龙舌兰)和阿罗卡特斯棘豆(一种桶状仙人掌)。这种储存的水的内部再分配会影响蒸腾流中的水分流动，蒸腾流是从土壤到根、茎和叶的路径，并导致非稳态(瞬时)效应。这样的瞬变效应。这可以通过在蒸腾流的电路模拟中加入电容器来考虑，在植物中很少受到关注，尽管在自然条件下，非稳态实际上是植物的规则，而不是例外。多汁植物，如沙枣和棘豆，利用景天酸代谢，二氧化碳吸收主要发生在夜间，温度较低，因此植物向空气中流失的水分较少。夜间吸收的二氧化碳会导致苹果酸的形成，从而导致渗透压的大幅增加。渗透压的这种增加会通过渗透作用影响水分的运动，这是一种以前没有包括在植物水分关系电路模拟中的复杂情况。将采用一种新的方法，允许合并这种非线性因素。医学研究中开发的新成像方法也将用于观察土壤中的根位置。利用电路模拟，将利用开发的用于求解电路的计算机程序来模拟不同位置的水的运动和水势。蒸腾流中的每个组件(如树叶)将被分配一个电容，该电容将通过存储电阻连接到血管组织的主轴向流。还将对沙漠多肉植物进行实地测量，以进一步解释沙漠多肉植物对水分胁迫和水分利用的关键适应。将这些数据综合到一个动态模型中，可以增强我们对植物细胞特性的定量理解，以及电容和渗透压在维持有利于植物在田间生存的水势方面的重要性，特别是当它们暴露在自然或人为的环境条件变化中时。

Water is the key to the growth and survival of desert plants. It can be stored in the shoots, which is especially apparent for succulent plants such as Agave deserti (the common desert agave) and Ferocactus acanthodes (a barrel cactus). Internal redistribution of such stored water can influence water flow in the transpiration stream, the pathway from the soil to the root, stem, and leaves, and lead to non-steady state (transient) effects. Such transient effects. which can be considered by incorporating capacitors in electrical circuit analogs of the transpiration stream, have received little attention for plants, although the non-steady state is actually the rule, not the exception, for plants under natural conditions. Succulent plants such as A. deserti and F. acanthodes employ Crassulacean acid metabolism, where CO2 uptake occurs predominantly at night when temperatures are lower and hence water loss from the plant to the air is less. The CO2 taken up at night leads to the formation of malate, with a consequent large increase in osmotic pressure. This increase in osmotic pressure influences water movement by osmosis, a complication that has previously not been included in electrical circuit analogs for plant water relations. A new method will be employed that allows incorporation of this non-linear factor. New imaging methods developed in medical research will also be used to observe root location in the soil. Using an electric circuit analog, water movement and water potential will be simulated at various locations with computer programs developed to solve electrical circuits. Each component (such as a leaf) in the transpiration stream will be assigned a capacitance, which will be connected through a storage resistance to the main axial flow of the vascular tissue. Field measurements of desert succulents will also be made to interpret further the key adaptations of desert succulents to water stress and water use. Synthesizing the data into a dynamic model should enhance our quantitative understanding of the cellular properties of plants and the importance of capacitance and osmotic pressure in maintaining water potentials favorable for plant survival in the field, especially when they are exposed to natural or man- made changes in environmental conditions.