Studies On Photosynthetic Characteristics And Canopy Management Of Triploid Chinese White Poplar Pulpwood

This paper was studied on the structural characteristics of Triploid Chinese White Poplar canopy and photosynthetic characteristics of leaves in the canopy with differents planting configuration and stand densities;Studied on carbon dioxide assimilation source/sink relation mechanism after girdling on phloem;Meanwhile, in order to get a reasonable canopy structure management technology, according to canopy structure characteristics, pruning the canopy of Triploid Chinese White Poplar; The main results as follows:(1) Leaf Area Index(LAI) and Extinction Coefficient (K) of the buttom canopy were reache maximum, K of the buttom canopy was arrived 0.89, more 0.07 than middle and top 0.005.In the growing period, the different layers in the canopy, Light Saturation Point (LSP) changed from 600μmol·m-2·s-1 to 1350μmol·m-2·s-1, Light Compensation Point (LCP) from 12μmol·m-2·s-1 to 33μmol·-2·s-1, the dark respiration(Rd) and apparent quantum yield (a) were changes within 17.4μmol·m-2·s-1 and 0.109 molCO2·mol-1, respectively; Leaves in east branch, the top of canopy and outside of branch, the LSP, LCP and maximum net photosynthetic rate(Pmax) were highest.The leaves of WUE were increase with stomatal conductance(Gs) increasing, but there were no difference between leaves in the different canopy positions.(2) Specific Leaf Weig(SLW) was changed with leaf development, showed increase-reduce-increase trend, with the depth in the vertical canopy, SLW decreased; Specific Leaf Area (SLA) was reduce-increase-reduce in the whole growing season;With the depth in the vertical canopy, leaf nitrogen increased;With the tree grow, leaf nitrogen was increase, then decrease, meanwhile, leaves in the utter was highest.In the growing period, leaf nitrogen and Pmax exists significant positive correlation.The non-structural carbohydrate (NSC) of leaves in different positions of canopy while its content was maximum in the mature period.(3) The tree growth and growth rate of Triploid Chinese White Poplar were different due to different planting configurations, diameter,height and volume had grow slowly during the first 5 years.Leaf area index and extinction coefficient of Uniform planting configuration higher than strip planting configuration in the whole growing season;But leaf nitrogen in strip configuration was more.Branches'angle and length increased with decreased stand density.Low-density tree could receive more light, had higher LSP and LCP; NSC of leaves was decrease then increase with decreasing stand density.(4) Leaf photosynthesis was lower after girdling tree, LSP changed from 815μmol·m-2·s-1 to 1529μmol·m-2·s-1.Girdling tree was cut off production from source to sink and caused the accumulation in the source leaves, especially starch.(5) In the growthing period, pruning tree to 1/2 and 1/3, SLW is lower than control and increase with canopy layer rise and the branch extension.Diameter, height, branch and stem biomass were higher than control when canopy shape ration was 1/4.