Study On Morphological And Physiological Responses Of Populus Tomentosa To Pruning

Pruning on 4-year-old plantations of Populus tomentosa with three degrees in Weixian (siteâ… ) and Bazhou (siteâ…¡) in Hebei Province was studied in this paper. The three pruning degrees were low-intensity P1, medium-intensity P2, strength-intensity P3 and the unpruned for control. Tree height, diameter at breast height, physiological parameters including net photosynthetic 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 the first year, 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 siteâ…¡; in the second year, the growth of diameter of P1 and P2 were bigger than CK and P3,the difference was distinct(P<0.01).2) Pruning speeded the height growth, and P1, P2 were conspicuously with CK(p<0.05) in the first year; the growth of height of PI was the biggest and it was conspicuously than others.3) Crown increments of different intensity pruning were fewer than CK in the first year of test and were greater in the second year, the canopy growth decreases with increasing pruning intensity.4) The leaf area index(LAI) changed significantly after pruning, and leaf density of pruned Populous stand increased while the LAI of CK decreased, and the LAI decreased in August in the second year. Thus, pruning can extend growing stage of trees.5) 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.6) Pruning improved the water use efficiency of Populus tomentosa Carr., water use efficiency of P1 and P2 were higher than CK and P3.7) Test showed that the P1 and P2 of the chlorophyll contents were slightly higher than CK and P3, pruning had no obvious effect on the chlorophyll content, but the P1 and P2 increased the chlorophyll a/b value, the value increased with the increase of sampling height.Considering from the growth, photosynthetic and physiological indices of Populus tomentosa Carr., branches in the bottom of canopy should be pruned after canopy closing.