修枝对毛白杨无性系生长、净光合速率和蒸腾速率的影响

以4年生毛白杨（Populus tomentosa Carr.）人工林为试验对象，在河北省威县苗圃（试验地I）和河北省霸州市万达林场（试验地II）开展修枝梯度为轻度修枝P1，中度修枝P2，强度修枝P3，以不修枝为对照的修枝试验，调查不同修枝强度毛白杨生长指标和不同冠层阳面叶片光合指标的变化，从生理机制解释修枝对毛白杨人工林生长的影响。结果表明：1）修枝第一年会影响胸径生长，随修枝强度增大影响增强，但轻度修枝和中度修枝与对照差异不显著，试验地I强度修枝与对照差异显著，试验地II强度修枝与对照差异不显著（P＞0.05）；2）修枝对毛白杨树高生长有一定促进作用，且轻度修枝和中度修枝与对照差异显著（P＜0.05）；3）修枝前后叶面积指数（LAI）变化较大，叶量随时间变化增多，在对照叶面积指数下降时修枝处理叶面积指数仍在增加，修枝能够延长树木生长期；4）修枝能提高毛白杨中上部叶片净光合速率（Pn）和蒸腾速率（E），有利于提高光合和物质合成能力，而对照的下部叶片净光合速率和蒸腾速率都处于比较低的水平。因此从生长和光合生理综合分析，毛白杨人工林郁闭后树冠下部需要适度修枝。

Effects of Pruning on Growth, Net photosynthesis Rate and Transpiration Rate of Populus tomentosa in Plantation

Pruning on 4-year-old plantations of Populus tomentosa with three degrees in Weixian （site I） and Bazhou （site II） of Hebei Province was studied in this paper.The three pruning degrees were low-grade P1,medium-grade P2,strength-grade P3 and the unpruned for control.Tree height,diameter at breast height,physiological parameters including net photosynthesis rate and transpiration rate in different canopies were measured,in order to explain the impact of pruning from the physiological mechanism.The results were：（1） Pruning inhibited the growth of diameter,in proportion to the increasing intensity of pruning.Difference in P1 and P2 were not significant with CK,while,P3 was significantly different with CK in site I,whereas not significant with CK in site II;（2） Pruning speeded the height growth,and P1,P2 were conspicuously with CK （P 0.05）;（3） The leaf area index（LAI） changed significantly after pruning,and leaf density of pruned Populous stand increased while the LAI of CK decreased.Thus,pruning can extend growing stage of trees;（4） Pruning improved net photosynthesis rate and transpiration rate of leaves in the middle and upper of crown,but these indices in the bottom crown were low at the same time.Considering from the growth,photosynthetic and physiological indices of Populus tomentosa,branches in the bottom of canopy should be pruned after canopy closing.