Studies on the formation of xylem embolism influencing tree survival

1.赤松对木质部空化的脆弱性松材线虫感染松材线虫的水分状况下降是由于栓塞物引起木质部导水性丧失所致。在感染松材线虫后，根和茎木质部开始比感染前更容易发生空化。感染松材线虫的松材线虫发生栓塞症与木质部脆弱性的改变密切相关。对木质部的磁共振成像(MRI)显示，随着病情的发展，木质部的栓塞区面积逐渐增大，并且不局限于接种线虫部位附近，而是遍及整个木质部。木质部栓塞病对遭受松材线虫病危害的松树是一种致命的打击。2.短叶松群落木质部空化的可硫化特性分布于高山高寒地带的短叶松群落。Norikura分为两种类型。一个是健康成长的社区，一个是受损的社区。后期的特点是，早春时针叶颜色变棕色。两个群落的木质部导水率在夏季都因空化而降低。秋季，健康杨木质部导水率恢复，而受害杨树木质部导水率没有恢复。10月份，受损树木的针叶似乎因风而脱水，因为它们没有被雪覆盖。也就是说，白杨群落的衰退似乎与全球变暖引发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.