Richards J H, Bliss L C
Department of Botany, University of Alberta, Edmonton, Alberta, Canada.
Oecologia. 1986 Apr;69(1):16-24. doi: 10.1007/BF00399032.
The degree of winter desiccation resistance exhibited by Larix lyallii Parl. was assessed by determination of water potential components and content of buds, xylem pressure potential (Ψ ) of twigs and amount of damage through winter at timberline in the Rocky Mountains of Canada. Comparative measurements were made on sympatric evergreen tree species to evaluate differences in winter desiccation avoidance and tolerance between evergreen and deciduous trees. Total (Ψ) and osmotic plus matric potentials (Ψ ) of L. lyallii buds were lowest in December (-5.0 to-5.3 MPa and-6.6 to-7.0 MPa, respectively) when temperatures were lowest. Bud Ψ and water content increased in late winter while Ψ of twigs continued to decline until March. The buds were isolated from the xylem from October through February, as indicated by large differences in water potential between the two organs during this time. Buds thus avoided desiccation as water was lost from the twigs. At the same time the buds were tolerant of very low Ψ and Ψ , a characteristic which is an important component of freezing damage resistance. Desiccation damage to buds of L. lyallii was much less than that to buds of similar-sized nearby trees of Abies lasiocarpa, although Ψ of both species was similar. The deciduous habit apparently confers a significant advantate to L. lyallii, which dominated the upper timberline sites, in reduced susceptibility to winter desiccation damage. Other deciduous timberline species might also benefit from this advantage where winter conditions are desiccating.Seedlings of L. lyallii were also studded for their winter desiccation resistance because they have a large component of non-deciduous (wintergreen) needles that are photosynthetically active through two growing seasons and must overwinter as mature tissue. Experimental exposure of these needles, which are normally protected by the snowpack, caused nearly complete mortality of the wintergreen needles when twig Ψ was only-3.9 MPa. The buds on these twigs were undamaged.
通过测定加拿大落基山脉树线处的芽的水势组分和含量、小枝的木质部压力势（Ψ）以及冬季的损伤量，评估了莱尔落叶松（Larix lyallii Parl.）的冬季抗干燥程度。对同域分布的常绿树种进行了对比测量，以评估常绿树和落叶树在冬季避免干燥和耐受干燥方面的差异。莱尔落叶松芽的总水势（Ψ）以及渗透势加基质势（Ψ）在12月温度最低时最低（分别为-5.0至-5.3兆帕和-6.6至-7.0兆帕）。芽的Ψ和含水量在冬末增加，而小枝的Ψ持续下降直至3月。10月至2月期间，芽与木质部隔离，这期间两个器官的水势差异很大。因此，当水分从小枝流失时，芽避免了干燥。同时，芽耐受极低的Ψ和Ψ，这一特性是抗冻害的重要组成部分。尽管两个物种的Ψ相似，但莱尔落叶松芽的干燥损伤远小于附近大小相似的紫果冷杉（Abies lasiocarpa）芽的损伤。落叶习性显然赋予了在树线上部占据主导地位的莱尔落叶松显著优势，使其对冬季干燥损伤的敏感性降低。在冬季条件干燥的地方，其他落叶树线物种可能也会从这一优势中受益。还对莱尔落叶松的幼苗进行了冬季抗干燥研究，因为它们有很大一部分非落叶（常绿）针叶，这些针叶在两个生长季节都具有光合活性，并且必须作为成熟组织越冬。这些通常被积雪保护的针叶经实验暴露后，当小枝Ψ仅为-3.9兆帕时，常绿针叶几乎全部死亡。这些小枝上的芽未受损。
