Kern Stephen O, Hovenden Mark J, Jordan Gregory J
School of Plant Science, University of Tasmania, Locked Bag 55, Hobart, Tas. 7001, Australia.
School of Plant Science, University of Tasmania, Locked Bag 55, Hobart, Tas. 7001, Australia. Corresponding author; email:
Funct Plant Biol. 2004 Jun;31(5):471-480. doi: 10.1071/FP03211.
The impact of differences in leaf shape, size and arrangement on the efficiency of light interception, and in particular the avoidance of photoinhibition, are poorly understood. We therefore estimated light exposure of branches in the cool temperate rainforest tree, Nothofagus cunninghamii (Hook.) Oerst., in which leaf shape, size and arrangement vary systematically with altitude and geographic origin. Measurements of incident photosynthetic photon flux density (PPFD) were made in the laboratory at solar angles corresponding to noon at summer solstice, winter solstice and equinox on branches collected from a common garden experiment. Tasmanian plants showed more self-shading than Victorian plants in summer and equinox. This was related to branch angle, leaf arrangement and leaf shape. Using a modelled light response-curve, we estimated the carbon assimilation rate and the flux density of excess photons at different incident PPFD. Victorian plants had higher predicted assimilation rates than Tasmanian plants in summer and equinox, but were exposed to substantially greater levels of excess photons. Because of the shape of the light-response curve, self-shading appears to reduce the plant's exposure to excess photons, thus providing photoprotection, without substantially reducing the carbon assimilation rate. This is dependent on both regional origin and season.
叶片形状、大小和排列差异对光拦截效率，尤其是对避免光抑制的影响，目前还知之甚少。因此，我们估算了凉爽温带雨林树种昆士兰假山毛榉（Nothofagus cunninghamii (Hook.) Oerst.）枝条的光照情况，该树种的叶片形状、大小和排列会随着海拔和地理起源而系统变化。在实验室中，针对从一个共同花园实验采集的枝条，在对应夏至、冬至和春分中午的太阳角度下，测量了光合有效辐射通量密度（PPFD）。塔斯马尼亚植株在夏季和春分时节比维多利亚州植株表现出更多的自我遮荫现象。这与枝条角度、叶片排列和叶片形状有关。利用模拟的光响应曲线，我们估算了不同入射PPFD下的碳同化率和过量光子通量密度。在夏季和春分时节，维多利亚州植株的预测同化率高于塔斯马尼亚植株，但它们受到的过量光子水平要高得多。由于光响应曲线的形状，自我遮荫似乎减少了植株对过量光子的暴露，从而提供了光保护，而不会大幅降低碳同化率。这既取决于区域起源，也取决于季节。
