Dissertation Research: Tree Size at Reproductive Onset and Leaf-level Photosynthesis in Malaysia Primary Rainforest Trees

该研究项目旨在探索树种大小（以繁殖开始时的高度衡量）与叶片光合作用光响应之间的关系。预测了热带雨林原始树木成树大小与最大光饱和光合速率（Pmax）呈正相关关系。这一预测来源于不同环境中光照水平与最大光合作用速率之间的普遍相关性，以及热带雨林冠层中存在的可预测的强光梯度。近年来对光照和遮荫条件的生理适应研究表明，热带雨林原始树木的光合适应相对有限。如果是这样的话，幼树的Pmax测量值应该与成年树的Pmax值相似，并且从幼树的光合作用测量中应该可以检测到所提出的异速生长关系。将测量35种树苗的最大光饱和光合速率（Pmax），这些树苗的大小和结构异速生长数据已收集。将评估所选树种幼树和成熟树之间的Pmax差异。研究中包括的每个属都跨越了很宽的大小范围，从林下小树到冠层树木，这使得测试系统发育差异成为可能。本研究首次尝试在异速生长环境下研究热带雨林树木的光合生理。

The proposed research project explores relationships between tree species size, measured as the height at onset of reproduction, and leaf-level photosynthetic light response. A positive relationship between adult tree size and maximal light-saturated photosynthetic rate (Pmax) among primary rainforest trees is predicted. This prediction derives from a general correlation across environments between light levels and maximum rate of photosynthesis, and the presence of a strong, predictable light gradient through the rainforest canopy. Recent studies of physiological acclimation to sun and shade conditions suggest that photosynthetic acclimation is relatively limited in primary tropical rainforest trees. If this is so, Pmax values measured for saplings should be similar to Pmax values for adult trees, and the proposed allometric relationship should be detectable from photosynthetic measurements on saplings. Measurement will be made of maximal light-saturated photosynthetic rate (Pmax) for saplings of 35 species for which size and structural allometric data have been gathered. Differences in Pmax between saplings and mature trees of selected species will be assessed. Each genus included in the study spans a wide size range, from understory treelets to canopy-level trees, making possible tests of phylogenetic differences. This study represents the first attempt to examine photosynthetic physiology of tropical rainforest trees in an allometric context.