Effects of environmental factors on permeability of soybean roots to water and solute

测定了热因素对大豆根系抗水流能力的影响。根系总阻力分为吸收（径向）阻力和传导（纵向）阻力。当根系温度高于13℃时，总阻力随根系温度的降低而增加，其增加速率与水黏度的增加速率相似。当温度低于13ºC时，总电阻急剧增加。因此，总阻力增加的主要原因是水粘度的温度依赖性。但其主要原因是在13ºC以下，细胞膜本身的通透性发生了变化。在任何范围内，导电电阻的变化速率与水粘度的变化速率相似。当温度在13 ~ 23℃范围内变化时，吸附阻力的变化速率与水粘度的变化速率相似。当温度低于13℃时，它急剧增加。由此可见，13 C是大豆根膜透水性的阈值，透水性的变化是总阻力急剧变化的主要原因。在13 ~ 23之间，吸收电阻占总电阻的比例基本稳定在75%，而在8时，吸收电阻占总电阻的比例急剧上升，达到90%。在大豆正常生长条件下，木质部的导电电阻在任何温度下都不可忽视。要模拟通过SPAC的水通量，必须考虑吸收电阻和导电电阻的温度依赖性。在本研究中，我们将重点放在低温条件下。在较高的温度条件下也可能存在类似的阈值，需要进一步研究。同时，还应找出植物生长适宜温度与这些阈值之间的关系。这项研究可以弄清楚植物生长的合适温度意味着什么。

The effect of thermal factors on resistance to water flow through soybean root system was measured. Total resistance of root system are divided to absorptive (radial) resistance and conductive resistance (=longitudinal) one. The total resistance increases with similar rate to water viscosity as temperature in root system decreases above 13ﾟC . While, the toal resistance increases sharply as temperature decreases below 13ﾟC.Thus, the principla cause of the increase in total resistance over 13ﾟC is the temperature dependency of water viscosity. However the principle cause is the change of permeability of cell membrane itself below 13ﾟC.The conductive resistance changes with similar rate to water viscosity as temperature changes in any range. The absorptive resistance changes with similar rate to water viscosity as temperature changes above 13ﾟC C to 23ﾟC.While, it increases sharply as temperature decreases below 13ﾟC.Thus, the temperature, 13ﾟC,is the threshold for water permeability of soybean root membrane and the change in the permeability seems to be the main cause of the sharp change of the total resistance.The contributing ratio of the absorptive resistance to the total resistance is almost constant at 75% from 13ﾟC to 23ﾟC,while the ratio increases sharply and increases up to 90% at 8ﾟC.The conductive resistance in xylem cannot neglect at any temperature for normal growing condition of soybean. Temperature dependency of both absorptive and conductive resistance must be taken into account to simulate the water flux through SPAC.In this research, we focused on lower temperature condition. Similar threshold could exist in higher temperature condition and should be found out. Also, the relation between appropriate temperature for plant growth and these thresholds should be found out. The research could make it clear what the proper temperature for plant growth means.