根电容能否用于预测土壤中的根质量？
Can root electrical capacitance be used to predict root mass in soil?
机构信息
The James Hutton Institute, Invergowrie, Dundee, UK.
出版信息
Ann Bot. 2013 Jul;112(2):457-64. doi: 10.1093/aob/mct044. Epub 2013 Mar 13.
BACKGROUND
Electrical capacitance, measured between an electrode inserted at the base of a plant and an electrode in the rooting substrate, is often linearly correlated with root mass. Electrical capacitance has often been used as an assay for root mass, and is conventionally interpreted using an electrical model in which roots behave as cylindrical capacitors wired in parallel. Recent experiments in hydroponics show that this interpretation is incorrect and a new model has been proposed. Here, the new model is tested in solid substrates.
METHODS
The capacitances of compost and soil were determined as a function of water content, and the capacitances of cereal plants growing in sand or potting compost in the glasshouse, or in the field, were measured under contrasting irrigation regimes.
KEY RESULTS
Capacitances of compost and soil increased with increasing water content. At water contents approaching field capacity, compost and soil had capacitances at least an order of magnitude greater than those of plant tissues. For plants growing in solid substrates, wetting the substrate locally around the stem base was both necessary and sufficient to record maximum capacitance, which was correlated with stem cross-sectional area: capacitance of excised stem tissue equalled that of the plant in wet soil. Capacitance measured between two electrodes could be modelled as an electrical circuit in which component capacitors (plant tissue or rooting substrate) are wired in series.
CONCLUSIONS
The results were consistent with the new physical interpretation of plant capacitance. Substrate capacitance and plant capacitance combine according to standard physical laws. For plants growing in wet substrate, the capacitance measured is largely determined by the tissue between the surface of the substrate and the electrode attached to the plant. Whilst the measured capacitance can, in some circumstances, be correlated with root mass, it is not a direct assay of root mass.
背景
插入植物基部的电极与生根基质中的电极之间测量的电容量通常与根质量呈线性相关。电容量常被用作根质量的测定方法，并且通常使用一种电模型进行解释，其中根表现为并联的圆柱形电容器。最近在水培中的实验表明，这种解释是不正确的，并且已经提出了一种新的模型。在这里，新模型在固体基质中进行了测试。
方法
测定了堆肥和土壤的电容作为含水量的函数，并且在温室或田间的沙或盆栽堆肥中生长的谷物植物的电容在对照灌溉条件下进行了测量。
主要结果
堆肥和土壤的电容随含水量的增加而增加。在接近田间持水量的含水量下，堆肥和土壤的电容至少比植物组织的电容大一个数量级。对于在固体基质中生长的植物，局部润湿茎基部周围的基质是记录最大电容的必要条件，最大电容与茎横截面积相关：离体茎组织的电容等于湿土中植物的电容。在两个电极之间测量的电容可以用一个电路模型来表示，其中组件电容（植物组织或生根基质）串联连接。
结论
结果与植物电容的新物理解释一致。基质电容和植物电容根据标准物理定律组合。对于在湿基质中生长的植物，测量的电容主要由基质表面和附着在植物上的电极之间的组织决定。虽然在某些情况下，测量的电容可以与根质量相关，但它不是根质量的直接测定方法。
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