杨树新生叶形态结构与光合作用的系统适应机制研究

Light is one of the most limiting resources to high photosynthetic efficiency in forest ecosystems. Intensive planting of forest plantations always causes mutual shading among individuals, and induces a significant decrease in light intensity. In addition, young and newly developed leaves in the upper canopy are exposed to high light, while mature leaves in the lower canopy are exposed to low light. In this situation, the systemic adaptation mechanism of woody plants to light is still unclear. Our previous studies of sorghum have demonstrated that changing the environmental factor of mature leaves affects the development and growth of newly leaves. Accordingly, we proposed assumption: the light environment of mature leaves in the lower canopy not only affects itself photosynthetic characteristics, but also affects the structure and function of newly developed leaves of the upper canopy in forest plantations. This study plans to adopt cuttings of typical Populus species as experimental material, and the shade-endurance will first be evaluated quantitatively. By breaking the research which just from single leaf level of photosynthesis-light response, dynamic and developmental acclimation of leaf will be analyzed via changing overall light environment in a single plant. Further, the systemic regulation of photosynthesis and the optimization of photosynthetic function will be discussed through changing local light environment. At last, all the data will be comprehensively analyzed to reveal the systemic adaptation mechanism of photosynthesis in woody plants, and to provide theory and practice support for high photosynthetic efficiency in poplar plantation.

林地光环境是树木高光效的主要限制因子。集约栽培下的人工林不但缺光，而且冠层与中下层的光照条件差异较大。那么，生长在这种异质性光环境中的树木是否会发生光合作用的系统调控？其适应机制是什么？我们在前期的研究中证实，高粱成熟叶周围的环境因子能影响新生叶的生长发育。由此提出假设：人工林中下层的弱光环境不但影响成熟叶的光合特性，很可能还会调控冠层新生叶的结构与功能。本课题拟在定量评价杨树耐阴性的基础上，突破前人多从单叶水平和改变整株照光条件来研究光合作用光响应的模式：首先探讨整株光环境调整时不同发育阶段叶片的光适应过程，弄清杨树成熟叶的动态适应机制及与新生叶发育适应的关系；然后通过调整植株局部光照，分析成熟叶在适应自身光环境的过程中对新生叶生长发育的影响，初步阐明杨树光合作用的系统调控及优化规律。研究结果将有助于理解杨树光合作用的系统适应机理，并为人工林的高光效及优质高产提供理论和实践支持。

人工林单位面积的木材产量及生态效益的提高与栽植密度关系密切，而合理密植是人工林优质高产的重要保障。增加种植密度必然会改变群体内的光环境，降低个体的光能利用而制约单株的光合效率。所以，人工林光环境是影响林业生产的关键因素。集约栽植的杨树人工林不但缺光，而且群体冠层与中下层的光照条件差异较大。基于此，研究人工林异质性光环境与树木生长发育的关系，对阐明人工林高光效、指导造林实践及提质增效具有重要意义。. 本项目以杨树无性系中金杨扦插苗为实验材料，分别采用盆栽与林地种植两种实验条件，通过人工模拟幼苗生长的不同光环境，探讨了异质性光环境中杨树光合作用的系统调控及优化适应规律。研究发现：（1）在盆栽条件下，与全曝光的植株相比，成熟叶遮阴而新生叶曝光的幼苗其新生叶的光合色素含量、光合潜力、气体交换参数和比叶重等明显下降，而且更接近于全遮荫植株的新生叶片，证实了杨树成熟叶周围的弱光环境不但能够影响到成熟叶自身的光合性能，同样也会影响到顶层新生叶的光合作用。（2）在林地条件下，与全曝光的植株相比，成熟叶遮阴而新生叶曝光的幼苗其新生叶的光合功能明显降低，表明大田环境中杨树成熟叶在适应自身周围光环境的过程中同样能够影响到冠层新生叶的生长发育及光合功能。（3）在林地条件下，随着植株中下部成熟叶遮荫数量的减少，对冠层新生叶生长发育的调控强度逐渐降低，说明这种影响程度与所处弱光环境成熟叶的数量有关，反映了杨树光合作用的系统调控存在阈值现象。这其中也可能牵涉到异质性光环境中植株光合作用的优化适应，单株为了弥补中下层叶片因弱光造成的碳同化损失而主动提高冠层叶片的光合功能。. 本研究在单株水平上探讨了异质性光环境中不同叶片光合作用的光响应差异及相互关系，揭示了木本植物光合作用的系统调控及优化适应，为今后开展人工林高光效的研究与实践提供了新视野。.