杨树幼林冠层光截获和光合效率的空间结构效应研究

In a forest community, the growth of individual tree is not only determined by its genetic characteristic but also influenced by the neighboring trees and the surrounding conditions. The spatial distribution of the individual trees reflect the relationship and interaction between individuals, and affect the ability of the occupation of growing space and the light interception. Light was found to be most closely related to wood production. Knowledge about the light use efficiency of an individual tree is thus essential to be establish optimal stand structures that increase tree resource use efficiency and stand level production. However, the research on the theoretical basis of the optimizing of stand structure is still limited. Poplar is an important tree species in Northern China, in this study, a field experiment will be conduct to study the effect of stand structure on the light interception and photosynthesis effect of the poplar trees. The experimental treatments include different planting scheme. The spatial structure will be quantified by creating structure parameters which are calculated on the tree size and position. The distribution of light and leaves, the photosynthesis characteristic, the structure of canopy and the tree growth will be measured to analyze the effect of spatial distribution and the competition on the light absorption, canopy structure, to analyze the relationship between the stand structure and the tree growth of individual trees, as to reveal the mechanism of how tree growth response to neighborhood spatial distribution, as well as to provide theoretical basis for the regulation and optimizing of stand structure.

在植物群体中，个体的生长不仅取决于自身的遗传特性，还受周围环境及其邻近树木的影响。树木的空间分布决定了个体之间的相互关系和相互作用，决定了其树冠生长范围及光能截获能力。光能截获是林分生产力形成的基础。合理营造林分空间结构可提高冠层对光能的利用效率，提高林分生产力。但目前缺乏从提高冠层光合效率对人工林林分结构进行调控和优化的理论基础。杨树是华北地区重要的造林绿化树种，本研究通过设计具有不同林分空间结构欧美杨幼树栽植方案，开展杨树冠层光合效率的空间结构效应研究。定量分析林分微结构单元的空间结构特征。并通过观测具有不同结构单元林分的光环境、叶面积、光合特性、冠层结构和林木生长等指标，分析个体间的距离、排列方式和邻体竞争对欧美杨光能利用、冠层结构和林木生长的影响；分析不同生长阶段与林分空间结构之间的相互关系。以揭示相邻木空间分布对个体生长产生影响的作用机制，为林分结构的调控及优化提供理论基础。

本研究通过设计4种具有不同结构单元的欧美杨幼树栽植试验，通过连续监测和模拟各模式下光合有效辐射的空间分布，对林分空间结构进行量化，进而研究林分空间结构对冠层光合效率的影响。在造林初期，CK的蓄积量显著高于4种非均匀栽植模式，比其余模式高21%-55.5%；随着林分的发展，4种栽植模式的单木生长速率高于CK，林分整体蓄积量的差异逐渐缩小，表明：在林分初期，密度因素是影响林分生产力的主要因素，但随着林分发展，单木之间的竞争强度越来越大，相邻木的空间分布对单木生长的影响越来越明显，林分空间结构对林地生产力的影响作用持续增强。除密度外，栽植模式对林分蓄积量也有一定影响，如相同密度下，模式b（一行满，二行栽2空1，三行空）比模式a（一行满，二三行栽1空2）的蓄积量高20.8%。在造林初期，CK的林分叶面积指数（LAI）最大的，比其余栽植模式高出4%-66.3%，即密度对林分蓄积量和林分LAI的影响更大。随着林龄的增加，在高密度林分中，林木生长衰退迹象较明显。不均匀结构单元内，单株不同方位LAI和冠幅受到相邻木分布方位的显著影响，呈非对称生长，但不受相邻木分布数量的影响。LAI与林分胸高段面积（BA）间呈极显著线性相关（P < 0.001, R2=0.916）。因此，在人工林中，相邻木的空间结构，尤其是相邻木的分布格局对林木生长有重要作用，对森林经营管理的启示是林分结构调控与优化应以增加林分内单木分布的随机性为导向。