Pearcy Robert W, Valladares Fernando, Wright S Joseph, de Paulis Eloisa Lasso
Section of Evolution and Ecology, Division of Biological Sciences, University of California, Davis, CA 95616, USA.
Oecologia. 2004 Apr;139(2):163-77. doi: 10.1007/s00442-004-1496-4. Epub 2004 Feb 7.
The crown architectures of 11 Psychotria species native to Barro Colorado Island, Panama were reconstructed from field measurements of leaf and branch geometry with the three-dimensional simulation model Y-plant. The objective was to assess the role of species differences in architecture in light capture and carbon gain in their natural understory environment. When species were grouped according to their putative light environment preference, the shade tolerant species were found to have a small but significantly higher efficiency of light capture for both diffuse and direct light as compared to the light demanding species. Within each grouping, however, there were few significant differences in light capture efficiency among species. The lower efficiencies of light demanding species was due to slightly higher self-shading and slightly lower angular efficiencies. Simulations of whole plant assimilation showed that light demanding species had greater daily assimilation in both direct and diffuse light due to the significantly greater light availability in the sites where light demanding species were found, as compared to those where shade tolerant species occurred. Among light demanding species, the above ground relative growth rate measured over a 1-year period by applying allometric equations for mass versus linear dimensions, was positively correlated with diffuse PFD and with mean daily assimilation estimated from Y-plant. For the shade tolerant plants, there was no significant correlation between RGR and mean daily assimilation or with any measure of light availability, probably because they occurred over a much narrower range of light environments. Overall, the results reveal a strong convergence in light capture efficiencies among the Psychotria species at lower values than previously observed in understory plants using similar approaches. Constraints imposed by other crown functions such as hydraulics and biomechanical support may place upper limits on light capture efficiency.
利用三维模拟模型Y-plant，通过对巴拿马巴罗科罗拉多岛原产的11种九节属植物的叶片和枝条几何形状进行实地测量，重建了它们的树冠结构。目的是评估树冠结构的物种差异在其自然林下环境中的光捕获和碳增益中的作用。当根据假定的光环境偏好对物种进行分组时，发现耐荫物种在漫射光和直射光下的光捕获效率虽小但显著高于喜光物种。然而，在每个分组中，物种间的光捕获效率几乎没有显著差异。喜光物种较低的效率是由于自我遮荫略高和角效率略低。整株植物同化的模拟表明，由于与耐荫物种所在地点相比，喜光物种所在地点的光照可用性显著更高，喜光物种在直射光和漫射光下的日同化量更大。在喜光物种中，通过应用质量与线性尺寸的异速生长方程在1年期间测量的地上相对生长率，与漫射光合光子通量密度以及从Y-plant估计的平均日同化量呈正相关。对于耐荫植物，相对生长率与平均日同化量或任何光照可用性指标之间没有显著相关性，可能是因为它们出现在更窄的光照环境范围内。总体而言，结果表明，与之前使用类似方法在林下植物中观察到的值相比，九节属物种在较低值的光捕获效率上有很强的趋同性。由其他树冠功能（如液压和生物力学支撑）施加的限制可能会对光捕获效率设置上限。
