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

这项拟议的研究项目探索了树种大小(以繁殖开始时的高度衡量)与叶片水平光合光反应之间的关系。预测了原始雨林树种的成树大小与最大光饱和光合作用速率(Pmax)之间的正相关关系。这一预测源于不同环境之间的普遍相关性，即光照水平和最大光合作用速率之间的相关性，以及穿过雨林树冠的强烈、可预测的光照梯度的存在。最近对日照和遮荫条件的生理适应研究表明，初级热带雨林树木的光合作用适应相对有限。如果是这样的话，幼树的Pmax值应该与成年树的Pmax值相似，并且所提出的异速生长关系应该可以从幼树的光合作用测量中检测出来。将测量35个树种的树苗的最大光饱和光合作用速率(Pmax)，这些树种的大小和结构异速生长数据已经收集。将评估选定树种的幼树和成熟树之间的Pmax差异。研究中包括的每个属的大小范围都很广，从林下小树到冠层水平的树木，这使得对系统发育差异的测试成为可能。这项研究是第一次尝试在异速生长的背景下检查热带雨林树木的光合作用生理学。

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.