植物体内水分传输机制新解说

New Explanation of Water Transport Mechanism in Plants

根系和叶肉细胞的渗透吸水能把水势差转化为驱动水分运行的动力,称之为渗透泵。通过两个渗透泵的协同作用所形成的合力,将土壤水分运送到植物顶端。根据双渗透泵协同运输原理,植物水分运输可以在连续水柱和不连续水柱两种状态下进行。当根系吸水速率大于蒸腾失水速率时,木质部为正压,水柱是连续的,水分运行方式以根系产生的正压力为主,由下向上整体推动。当蒸腾失水速率大于根系吸水速率时,木质部为负压,水柱呈不连续状态,不连续水柱是以分段提升的阶梯式移动方式运输,这种方式既不依靠连续水柱,也不需要巨大的负压。负压形成的空穴使水柱分成若干段,每一段的顶端凹面产生的毛管力与重力平衡,使木质部中的水分不会因重力作用而下移,成为分段移动的必备条件。空穴的实质是水分亏缺形成负压导致的结果,只要木质部压力恢复,空穴即消除。空穴的存在不会阻断水分的运输,只是使水分移动选择了另一种方式。

The osmotic absorbent energy of root system and mesophyll cells converts water potential difference into the driving force of water operation, which is called osmotic pump. The combined force formed by the synergy of the two osmotic pumps transports soil moisture to the top of the plant. According to the double osmotic pump cooperative transportation principle, water transportation in plant can be carried out in two states: continuous water column and discontinuous water column. When the root’s water absorption rate is greater than the transpiration water losing rate, the xylem is in the state of positive pressure and the water column is continuous. The water operation mode is mainly driven by the positive pressure generated by the root system and is pushed upward as a whole. When the transpiration water losing rate is greater than the root’s water absorption rate, the xylem is in the state of negative pressure, and the water column is discontinuous. The discontinuous water column is transported in a stepped lifting manner, which neither relies on continuous water column nor requires huge negative pressure. The holes made by negative pressure divided the water column into several sections, and the capillary force and gravity balance generated by the concave surface at the top of each section keep the water in the xylem not to move down due to gravity, which becomes an indispensable condition for segmented movement. The essence of holes is the result of negative pressure created by water deficiency. As long as the pressure is restored, the holes are eliminated. The existence of holes does not prevent water transport, but allows it to move in a different way.