三倍体毛白杨无性系B301幼树树冠结构特征研究

为探究以树冠结构为特点的毛白杨幼树生物学特征，为人工幼林抚育管理提供参考，以3年生三倍体毛白杨优良无性系B301人工林为对象，从分枝数、基径、枝条长度、着枝高度、方位角、分枝角度、生物量等角度，分析其树冠结构特征。结果表明，三倍体毛白杨B301不同级别侧枝数量差异显著（P<0.05），二级枝条最多，一级枝条和二级枝条占总侧枝数量的94.7%；不同方位分枝数量差异显著（P<0.05），东北方位最多，为总分枝数的39.3%，但单枝及单叶生物量在方位上差异不显著（P>0.05）；各级侧枝枝条基径、着枝处直径、着枝高度、枝条长度差异显著（P<0.05），但不同方位间无显著差异（P>0.05）；树冠在垂直结构上分层明显，其侧枝集中在树干中部树高51.1%的范围；单株地上总生物量（干重）为34 741.9 g，枝条及叶片的生物量分别占地上部分总生物量的33.8%和11.2%；枝条及叶片生物量与所在枝条基径相关性最大，通过幂函数构建枝条基径与枝、叶生物量回归方程，回归关系显著（P<0.000 1）。因此，三倍体毛白杨B301树冠水平空间大、垂直层次分明，是比较理想的冠型，研究结论可为其合理修枝方式和强度的确定提供依据。

Characteristics of Crown Architecture of Young Triploid Populus tomentosa B301 Clones

The objectives of this study were to explore the biological characteristics of young Populus tomentosa with crown structure as the characteristics,and to provide references for tending and management of young plantations.Taking three-year-old fast-growing triploid P.tomentosa B301 clones as the research objects,the characteristics of crown structure were analyzed from the aspects of lateral branch numbers,branch basal diameter,branch length,height to ground or branch bottom,orientation,branch inclination and biomass.The results showed that there were significant differences in the number of lateral branches among different orders of P.tomentosa B301 clones (P<0.05).The number of secondary branches was the most,and the first and second order branches accounted for 94.7% of the total.There were significant differences in the number of branches in different directions (P<0.05).The number of lateral branches in the northeast was the largest,accounting for 39.3% of the total.However,there were no significant differences in biomasses of single branch and single leaf (P>0.05) in different direction.There were significant differences in basal diameter,diameter of branching site,height and length of branches among different levels of lateral branches (P<0.05),but there was no significant difference in different directions (P>0.05).The vertical structure of the crown was obviously layered,and its lateral branches were concentrated in the middle of the trunk,51.1% of tree height.The total aboveground biomass (dry weight) of 3-year-old triploid P.tomentosa B301 clones was 34 741.9 g,and the biomass of branches and leaves occupied 33.8% and 11.2% of the total biomass of the upper part respectively.The regression equations of the branch basal diameter and branch and leaf biomass were constructed by power functions,and the regression relationships were significant (P<0.000 1).Therefore,the crown of triploid P.tomentosa B301 clones with large horizontal space and clear vertical layers is an ideal crown type.The research conclusion can provide the basis for determining the reasonable pruning methods and strength.