Department of Biological Sciences, University of Waikato, Private Bag 3105, Hamilton, New Zealand.
Ann Bot. 2013 Mar;111(3):479-88. doi: 10.1093/aob/mcs289. Epub 2012 Dec 21.
A trade-off between shade tolerance and growth in high light is thought to underlie the temporal dynamics of humid forests. On the other hand, it has been suggested that tree species sorting on temperature gradients involves a trade-off between growth rate and cold resistance. Little is known about how these two major trade-offs interact.
Seedlings of Australian tropical and cool-temperate rainforest trees were grown in glasshouse environments to compare growth versus shade-tolerance trade-offs in these two assemblages. Biomass distribution, photosynthetic capacity and vessel diameters were measured in order to examine the functional correlates of species differences in light requirements and growth rate. Species light requirements were assessed by field estimation of the light compensation point for stem growth.
Light-demanding and shade-tolerant tropical species differed markedly in relative growth rates (RGR), but this trend was less evident among temperate species. This pattern was paralleled by biomass distribution data: specific leaf area (SLA) and leaf area ratio (LAR) of tropical species were significantly positively correlated with compensation points, but not those of cool-temperate species. The relatively slow growth and small SLA and LAR of Tasmanian light-demanders were associated with narrow vessels and low potential sapwood conductivity.
The conservative xylem traits, small LAR and modest RGR of Tasmanian light-demanders are consistent with selection for resistance to freeze-thaw embolism, at the expense of growth rate. Whereas competition for light favours rapid growth in light-demanding trees native to environments with warm, frost-free growing seasons, frost resistance may be an equally important determinant of the fitness of light-demanders in cool-temperate rainforest, as seedlings establishing in large openings are exposed to sub-zero temperatures that can occur throughout most of the year.
在高光照下，树木的耐荫性和生长之间存在权衡关系，这种权衡关系被认为是潮湿森林时间动态变化的基础。另一方面，有人认为，树种在温度梯度上的分异涉及到生长速度和抗寒性之间的权衡关系。目前还不太清楚这两个主要的权衡关系如何相互作用。
在温室环境中培养澳大利亚热带和凉爽温带雨林树种的幼苗，以比较这两个集合体中生长与耐荫性的权衡关系。测量生物量分布、光合能力和导管直径，以研究物种在光需求和生长速度方面差异的功能相关性。通过对茎生长的光补偿点进行野外估计来评估物种的光需求。
需光性强和耐荫性强的热带物种的相对生长率（RGR）差异显著，但温带物种的这种趋势不明显。这一模式与生物量分布数据相吻合：热带物种的比叶面积（SLA）和叶面积比（LAR）与补偿点呈显著正相关，但凉爽温带物种则不然。塔斯马尼亚需光者生长缓慢、SLA 和 LAR 较小，与导管狭窄和潜在边材导水率低有关。
塔斯马尼亚需光者保守的木质部特征、较小的 LAR 和适中的 RGR 与抗冻融栓塞的选择一致，牺牲了生长速度。在温暖、无霜生长季节的环境中，对光的竞争有利于喜光树木的快速生长，而在凉爽的温带雨林中，光需求者的适应能力同样重要的决定因素可能是抗冻性，因为在大开口处建立的幼苗会暴露在全年大部分时间都会出现的零度以下的温度中。
