Feild Taylor S, Brodribb Tim
Department of Organismic and Evolutionary Biology, Harvard University, 02138, Cambridge, MA, USA.
Department of Plant Science, University of Tasmania, GPO Box 252-55, 7001, Hobart, Australia.
Oecologia. 2001 May;127(3):314-320. doi: 10.1007/s004420000603. Epub 2001 May 1.
The effect of freezing on stem xylem hydraulic conductivity and leaf chlorophyll a fluorescence was measured in 12 tree and shrub species from a treeline heath in Tasmania, Australia. Reduction in stem hydraulic conductivity after a single freeze-thaw cycle was minimal in conifers and the vessel-less angiosperm species Tasmannia lanceolata (Winteraceae), whereas mean loss of conductivity in vessel-forming angiosperms fell in the range 17-83%. A positive linear relationship was observed between percentage loss of hydraulic conductivity by freeze-thaw and the average conduit diameter across all 12 species. This supports the hypothesis that large-diameter vascular conduits have a greater likelihood of freeze-thaw cavitation because larger bubbles are produced, which are more likely to expand under tension. Leaf frost tolerances, as measured by a 50% loss of maximum PSII quantum yield, varied from -6 to -13°C, indicating that these species were more frost-sensitive than plants from northern hemisphere temperate forest and treeline communities. There was no evidence of a relationship between frost tolerance of leaves and the resilience of stem water transport to freezing, suggesting that low temperature survival and the resistance of stem water transport to freezing are independently evolving traits. The results of this study bear on the ecological importance of stem freezing in the southern hemisphere treeline zones.
在澳大利亚塔斯马尼亚树线石南荒原的12种树和灌木物种中，测定了冷冻对茎木质部水力传导率和叶片叶绿素a荧光的影响。在针叶树和无导管被子植物物种披针叶 Tasmannia（林仙科）中，单次冻融循环后茎水力传导率的降低最小，而形成导管的被子植物中传导率的平均损失在17%-83%范围内。在所有12个物种中，冻融导致的水力传导率损失百分比与平均导管直径之间观察到正线性关系。这支持了以下假设：大直径维管束更有可能发生冻融空化，因为会产生更大的气泡，这些气泡在张力作用下更有可能膨胀。通过最大PSII量子产率损失50%来衡量的叶片抗冻性在-6至-13°C之间变化，这表明这些物种比北半球温带森林和树线群落的植物对霜冻更敏感。没有证据表明叶片的抗冻性与茎水分运输对冷冻的恢复能力之间存在关系，这表明低温存活和茎水分运输对冷冻的抗性是独立进化的性状。本研究结果揭示了南半球树线区域茎冷冻的生态重要性。
