Effects Of Pruning On Physiology Of Poplar Clone (Populus×Euramericana Cv.'74/76')

As a basic measurement for forest management, pruning has important roles on tree growth. Pruning can promote the growth of trees, improve the yield and quality of trees, improve the tree canopy type, increase the satisfactory degree of trunk, enhance the sapling tree vigor, uniform distribution of the thick branches and form distinct branches. Pruning also can cut competing branches and leggy branches, so can improve the survival rate.In this thesis, Europe 107 Poplar(Populus×euramericana cv,'74/76') as the research object, we measured various physiological indices of Europe 107 Poplar during the growing season(June to September).These physiological indices include stem sap flow, net photosynthetic rate(Pn), stomatal conductance(Gs), intercellular CO2 concentration (Ci),transpiration rate (Tr), leaf water potential (LWP), instantaneous water use efficiency (WUE), leaf water content (LWC), leaf water retention capacity (RWL), leaf water saturation deficit (WSD) and leaf relative water content (RWC) Etc. The experiment has two experimental sites:one chooses 4a poplar as the research object, and the other 6a poplar. There are 3 treatment levels:the CK (unpruned), P1 (1/3 crown was pruned) and P2(2/3 crown was pruned).The results are:1) The variation of Flux and Velocity is P1>CK>P2 during dry season (June to August).But, in regular month of September, the variation is CK>P1>P2.The Flux and Velocity of P1 are almost same during drought or normal months. This indicates that the stem sap flow of poplar is maintained at a certain low level by proper pruning (P1).And, the capability of counteracting drought observably is increased after pruning. In drought or normal state. Flux and Velocity of P2 is always in a very low level. This shows that, because of over-pruning and losing too much branches and leaves, water absorption capacity of P2 is reduced.2)In 2010,the rainfall of the experimental site is increased in overall, but is still in dry sate compared with previous years. We repeated measure the Flux and Velocity of 6-year-old 107 poplar. The value and variation of stem sap flow are basically same between CK and P1.Compared with 2009,the stem sap flow of PI is basically unchanged, but the CK is slightly increased. These show that, during 2010, the water content of experiment site is an adequate supply of P1 but not CK. The result of test verifies the accuracy of the value and variation of stem sap flow measured during 2009.3) Throughout the growing season, the order of net photosynthetic rate (Pn) is CKP1>P2 under different pruning intensity. This tells us that intercellular CO2 is consumed faster by photosynthesis than the addition of stomatal conductance. It also shows that the intercellular CO2 concentration with the net photosynthetic rate and stomatal conductance was significantly negatively correlated relationship.6) Throughout the growing season, the order of transpiration rate (Tr) is CKP1>P2. This shows that pruning increases drought resistance of single leaf. This change may be because pruning measures change the internal mechanism of tree or leaf.