Can root electrical capacitance be used to predict root mass in soil?
Can root electrical capacitance be used to predict root mass in soil?
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DOI：
10.1093/aob/mct044
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发表时间：
2013-07-01
期刊：
影响因子：
4.2
通讯作者：
White, P. J.
中科院分区：
文献类型：
--
作者：
Dietrich, R. C.;Bengough, A. G.;White, P. J.
在植物根部插入的电极和生根基质中的电极之间测量的电容通常与根质量呈线性相关。电容通常被用作根质量的测定，并且通常使用一个电学模型来解释，其中根表现为并联的圆柱形电容器。最近的水培实验表明，这种解释是不正确的，并提出了一种新的模型。在这里，新模型在固体衬底上进行了测试。测定了堆肥和土壤的容量作为含水量的函数，并在不同的灌溉制度下测量了在沙土或盆栽堆肥中生长的谷类植物在温室或田间的容量。随着含水量的增加，堆肥和土壤的电容增大。当含水量接近田间容量时，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来说，将茎基部周围的基质局部润湿是记录最大电容的必要和充分条件，这与茎的横截面积有关：切除的茎组织的电容等于湿土中的植物的电容。在两个电极之间测量的电容可以建模为一个电路，其中组件电容器（植物组织或生根基质）串联在一起。结果与植物电容的新物理解释一致。基片电容和植物电容根据标准物理定律组合。对于生长在潮湿衬底中的植物，所测量的电容在很大程度上取决于衬底表面和附着在植物上的电极之间的组织。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。
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.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.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.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.