Clearwater Michael J, Gould Kevin S
Plant Sciences Group, School of Biological Sciences, University of Auckland, Private Bag 92019, Auckland, New Zealand.
Oecologia. 1995 Nov;104(3):363-371. doi: 10.1007/BF00328372.
Leaf orientations and light environments were recorded for 40 juvenile Pseudopanax crassifolius trees growing in New Zealand in a partially shaded, secondary forest environment. Efficiencies of interception of diffuse and direct light by the observed leaf arrangments were calculated relative to those of three hypothetical leaf arrangements. Canopy gaps above the study plants were unevenly distributed with respect to azimuth and elevation above the horizon. Our results indicate that photosynthetically active radiation (PAR) received from the sides is more important than that received from directly above. In 33 of the plants leaf orientation was found to be significantly clustered towards one azimuth. The mean azimuth and the mean angle of declination were different for each plant. Leaves were steeply declined, and oriented towards the largest canopy gap at each site. Steep leaf angles reduced interception of direct and diffuse PAR when compared to interception by plant with a hypothetical horizontal leaf arrangement. When compared to a hypothetical arrangement with steep leaf declination and a uniform azimuth distribution, the observed leaf arrangement increased the efficiency of interception of diffuse PAR, but had a variable effect on the interception of direct PAR. Results indicate that the developing leaves of juvenile P. crassifolius orient towards the strongest sources of diffuse light, regardless of their value as a source of direct light. By maximising diffuse light interception while reducing direct light interception, leaf orientation may be a partial determinant of the types of habitats exploited by this species. This study emphasises the importance of considering diffuse light interception for plants growing in partially shaded environments.
在新西兰一片部分遮荫的次生林环境中，对40棵粗叶拟五加幼树的叶片朝向和光照环境进行了记录。相对于三种假设的叶片排列方式，计算了观察到的叶片排列对漫射光和直射光的截获效率。研究植株上方的林冠间隙在地平线以上的方位和高度上分布不均匀。我们的结果表明，从侧面接收的光合有效辐射（PAR）比从正上方接收的更重要。在33株植株中，发现叶片朝向显著聚集在一个方位上。每株植物的平均方位和平均偏角都不同。叶片急剧倾斜，并朝向每个地点最大的林冠间隙。与具有假设水平叶片排列的植株相比，陡峭的叶片角度减少了对直射和漫射PAR的截获。与具有陡峭叶片偏角和均匀方位分布的假设排列相比，观察到的叶片排列提高了对漫射PAR的截获效率，但对直射PAR的截获有不同的影响。结果表明，粗叶拟五加幼树发育中的叶片朝向最强的漫射光源，而不管其作为直射光源的价值如何。通过最大化漫射光截获同时减少直射光截获，叶片朝向可能是该物种所利用栖息地类型的一个部分决定因素。这项研究强调了考虑部分遮荫环境中生长的植物对漫射光截获的重要性。
