Studies on the formation of xylem embolism influencing tree survival

1.赤松木质部空洞化的脆弱性松材线虫病松树的水分状况下降是由于栓塞导致木质部丧失导水率所致。感染松材线虫后，根和茎木质部开始比感染前更容易受到空化。松材线虫病后松树栓塞的发生与木质部脆弱性的改变密切相关。木质部的磁共振成像（MRI）显示，木质部的栓塞面积增加，随着疾病的发展，并不局限于附近的线虫接种部分，但蔓延到整个木质部。木质部栓塞对遭受松材线虫病的松树是致命的打击。2.白皮松木质部空洞的脆弱性分布在高山区的白皮松群落。Norikura分为两种类型。一个是健康成长的社区，另一个是受损的社区。后来的特点是，针的颜色变化棕色在早春。在夏季，两种群落的沙枣木质部导水率均因空化作用而降低。秋季，健康的白皮松木质部导水率有所恢复，而受害的白皮松木质部导水率没有恢复。十月，受损树木的针叶似乎因风而枯萎，因为它们没有被雪覆盖。也就是说，白皮松群落的衰退可能与全球变暖引起的积雪深度变化有关。

1.Vulnerability to xylem cavitation in Pinus densifloraDecrease in water status of Bursaphelechus xylophilus infected-pine is due to losing hydraulic conductivity of xylem caused by embolism. After infection with pine wood nematodes root and stem xylems began more vulnerable to cavitation than before infection. Occurrence of embolism in B.xylophilus infected-pine is closely related to alteration of xylem vulnerability. Magnetic resonance imaging (MRI) of xylem showed that embolized area of xylem increased with development of disease and was not limited in the vicinity of nematode inoculated-portion but spread over the xylem. Xylem embolism deals pines suffered from pine wilt disease a fatal blow.2.Vulnerability of xylem cavitation in Pinus pumilaCommunities of Pinus pumila distributing in alpine zone of Mt. Norikura are divided into two types. One is healthy growing community and another is damaged community. Later is characterized that the needle color changes brown in early spring. Xylem hydraulic conductivities of P.pumila in both of communities decreased caused by cavitation during summer. In autumn xylem hydraulic conductivity of healthy P.pumila recovered but not in damaged P.pumila. In October needles of damaged trees seemed to dehydrate caused by wind because they have not covered with snow. Namely, decline of P.pumila community seems to relate to the alteration of snow depth triggered by global warming.