Mechanisms of Xylem Embolism in Tree Species

木质部的栓塞是指充满空气的木质部导管（管胞和/或血管）的存在，它可以导致水输送能力的显著降低。这反过来又会对植物的水分平衡产生不利影响，导致生长减少和枯死。在佛蒙特州北部的糖枫（Acersaccharum）树木栓塞的初步研究中，Sperry和Tyree发现，在冬季，树苗的木质部栓塞超过70%，许多小树枝失去了所有的导水能力。冬季栓塞的逐渐恢复发生在春季，并与木质部正压力的发展有关。在他们提出的研究中，Sperry和Tyree将确定冬季栓塞和恢复现象在共同发生的树种中有多普遍，这些树种代表了环状和弥散多孔被子植物和针叶树。这将在资助期间对每个物种的栓塞水平进行全年监测的背景下进行。通过实地和实验室操作，他们打算确定环境条件与诱发栓塞及其逆转之间的因果关系。这些信息将指导他们评估木质部栓塞在树种生态耐受性中的重要性，并解释物种枯死和衰退的事件。这项研究可能对造林实践产生重要影响，包括建立人工林和现有林分的管理，特别是在冬季伤害普遍存在的地区。通过确定栓塞诱导机制，本研究还将评估栓塞在环境胁迫对树木健康影响中的重要程度。

Embolism in the xylem of plants is the presence of air- filled xylem conduits (tracheids and/or vessels) and it can lead to a significant reduction in water transport capacity. This in turn can adversely influence the water balance of the plant causing reduction of growth and dieback. In a preliminary study of embolism in sugar maple (Acersaccharum) trees in northern Vermont, Sperry and Tyree found that during the winter the xylem of saplings became over 70% embolized, with many small twigs losing all of their water conducting capacity to embolism. Gradual recovery from winter embolism occurred during the spring and was associated with the development of positive xylem pressures. In their proposed research, Sperry and Tyree will determine how widespread the phenomenon of winter embolism and recovery is in co-occurring tree species representing ring-and diffuse-porous angiosperms, and conifers. This will be done in the context of year-round monitoring of embolism levels for each species over the period of funding. Through field and laboratory manipulations they intend to determine the causal link between environmental conditions and the induction of embolism, as well its reversal. This information will guide them in assessing how important xylem embolism is in the ecological tolerance of tree species, and in explaining episodes of species dieback and decline. This research may have important consequences for silvicultural practices, including the establishment of plantations and management of existing stands, especially in regions where winter injury is prevalent. By determining the mechanism of embolism induction, this research will also evaluate how important embolism is in the influence of environmental stress on tree health.