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

测定了热因子对大豆根系水流阻力的影响。根系总阻力分为吸收阻力（径向）和传导阻力（纵向）。当根系温度降低到13 ℃以上时，总阻力以与水分粘度相似的速率增加。当温度低于13 ℃时，总阻力急剧增加。因此，13 ℃以上总阻力增加的主要原因是水粘度的温度依赖性。但其主要原因是细胞膜本身的渗透性在13 ℃以下发生了变化。在任何温度范围内，导电电阻的变化率与水的粘度变化率相似。当温度在13 ℃以上变化到23 ℃时，吸收阻力以与水粘度相似的速率变化。而当温度降低到13 ℃以下时，吸收阻力急剧增加。因此，温度13 ℃，是大豆根膜透水性的阈值，透水性的变化是引起总阻力急剧变化的主要原因，吸收阻力对总阻力的贡献率为0.0001在13 ~ 23 ℃范围内，总电阻几乎恒定在75%，而在8 ℃时，总电阻率急剧增加，高达90%。在模拟SPAC的水通量时，必须同时考虑吸收电阻和传导电阻的温度依赖性。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。此外，还应找出植物生长的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适当温度意味着什么。

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.