Nodal Architecture And Hydraulic Function Of Some Broad-Leaved Trees

The paper studied some nodes of one year old twigs of trees grown well in the Beijing Forestry University. Nodal electrical resistance, PLC, anatomical function, contact angles and holocellulose and lignin content of some broad-leaved tree were studied with the means of physiology and anatomy, which aimed to elucidate nodes'effect on fight with drought, the safety of hydraulic system.The electrical resistance measurement showed that with the water stress got more and more serious, embolism extent and electrical resistance increased in the above internode when cut node. The difference of embolism repair existed in different segments and treatment showed clearly. Because the above node of being cut node can't repair embolism, then got into brownness and died, what's more, electrical resistance can't showed, which indicated it was cut node that made it difficult for embolism repair. Especially when water waned serious embolism repair can't process. Although the internodes of reserved node embolized serious, it had definite function of repair, which indicated reserved node made repair easy. The change of electrical resistance reflected the condition of water flowing and embolism. That was to say, the electrical resistance being less indicated embolism not serious and water flowing more smoothly, and the reverse is also true. The change of electrical resistance was related to anatomical structure, contact angles, chemical substances and so on.It has the space difference of xylem anatomical structure between internodes and nodes in morphology direction. The vessels of internodes were more homogeneous and internal diameter wider, whereas the differentiation of nodal cells was different. In nodes, the middle and smaller vessels increased. The PLC value of nodes was less than internodes'. Because the content of cellulose were less and contact angles bigger, water flowing velocity get slow. The narrower the vessels, the slower water flowed, and there were many coiled vessels in nodes, which resulted in wasting more time, restricting water flowing. So, water in nodes didn't lost easily, and the change of electrical resistance slower.The difference of hydraulic architecture between nodes and internodes resulted in their different meaning .Internodes were responsible for watering transporting mainly. Because of conducting efficiently, trees'every parts get water. But inter-diameter of their vessels were wider, embolism happened easily. Node was"constrain zones"which xylem was complex, and it wasted more time when water flowed through nodes. A series of"constrain zones"of shoots prevented gas embolism and microorganism diffusing, ensuring smooth and safety of hydraulic system.