Further Studies On The Embolism Repair In The Xylem Of Several Woody Plants

Cavitation and embolism are common events in plants and water stress is the most common of which induce cavitation. Cavitation is induced by air seeding, which can occur through the pores of pit membranes. It might also be caused by tiny air bubbles adhering to cracks in vessel walls.Following daily cavitation the refilling of embolized conduits is common in both woody and herbaceous plants even when the water in neighboring conduits is under tension. Dissolution of gas is regarded as the primary mechanism of daily embolism repair.We did experiments with several woody plants (angiosperm and gymnosperm plants). In our experiments there are not only phenomena that bubbles in small conduits kept contracting but also bubbles in big conduits kept expanding, some times later, it contracted too. Spherical bubbles mainly emerged from place where woody rays existed, and grew up continually. When we compare the amount of the gas in and out conduits in one view , the amount of the gas was equal in different periods of rewetting, air in the embolismed conduits entered the spherical bubbles at the end.According to the analysis, air dissolution and air transfer were both accounted for the embolism repair at the beginning, but at the end there was only air dissolution. Air in small conduits entered big conduits and spherical bubbles in out sections, and air in big conduits could came into spherical bubbles too. Air in embolismed conduits entered the spherical bubbles at the end. According to this, we can deduce that in alive trees air moved from embolismed conduits (tracheids) to pith, air transfer and air dissolution maybe both accounted for embolism repair.According to the conception of contact angle, it maybe has some relation with embolism repair. We drew and measured different plant's contact angle, the results showed that they were indeed different in different trees. In different seasons, the contact angle was different too. In summary it was big in winter and spring, small in summer and autumn. When the angle is small, embolism repair time is short, and when it is big, embolism repair time is long. So contact angle maybe one of reasons that cause embolism repair.