An Experimental Study Of Light Interception And Photosynthesis Product For3D Virtual Tall-spindle Apple Canopy In Loess Plateau Region Of China

Three tall spindle Fuji and Gala apple trees were used as material. The structures of threetrees of each cultivar were digitized to obtain3D representations of foliage geometry.Within-tree foliage distribution was compared with shoot demography, number of leaves pershoot and mean individual leaf area. We estimated branch and tree light interception fromsilhouette to total leaf area ratios （STAR） and net photosynthetic rates. We assessed spatialdistribution of leaves and leaf functions affect the light interception and photosyntheticcapacities of trees contributions at the branch and tree scales in two apple cultivars byestimating their branch and tree capacities and comparing them with outputs fromphotosynthesis functional–structural plant model. Main obtained results are as follows:A photosynthesis functional–structural plant model is presented. Between DPAR andDSTAR nolinear regression equation was found for light distribution model （DPAR=29.354×exp（-0.129/DSTAR））.From this experiment, useful linear regression equation between N_aand DPAR for leafphysiological model （Fuji: N_a=0.0668DPAR+0.8629, Gala: N_a=0.0639DPAR+0.7969） werederived. Between N_aand P_max, linear regression equation were found for leaf photosynthesismodel (Fuji: P_max=6.5476N_a+2.8751, Gala: P_max=4.7885N_a+2.8162). The apparent quantumefficiency and maximum photosynthesis rate of Fuji leaves were higher than gala leaves.Model outputs were compared with data acquired in the field.The Daily net photosynthetic of Fuji and gala trees were1550.33mmol CO₂and1300.31mmol CO₂. Daily variation of photosynthesis rate at tree scales shows a monopeak curve.We zone tree crown into different parts: up, middle and down crown base on leavesvertical positions or inner and outer crown base on leaves horizontal positions. The fuji STARwere significantly lower than gala in up, middle and down crown. Fuji have identical daily netphotosynthetic rates with Gala. The gala STAR were significantly higher than Fuji in innerand outer crown. Gala STAR of outer crown was significantly higher than Fuji. Daily netphotosynthetic rates of Fuji were higher than gala, but it was no statistics difference betweenFuji and Gala inner and outer crown. STAR value of all type of Fuji and Gala shoots is between0.091and0.263, and STARvalue of BL and VL is higher than other shoots. Only STAR of VS showed difference oncultivars. Daily net photosynthetic rates of all type of Fuji and Gala shoots is between23.63and123.46mmol m-2, and Daily net photosynthetic rates of BL and VL is higher than othershoots. Except VS, daily net photosynthetic rates of Fuji shoots was significantly higher thanGala.An analysis of the virtual switches of foliage distribution or leaf function showed thatdifferences in leaf spatial distribution and functions had additive effects that accounted for thelower photosynthetic rates of branches and trees of ‘Gala’ compared with ‘Fuji’. Leafdistribution had a more important role at the branch scale than at the tree scale, but the leaffunction effect exceeded the leaf distribution effect at both scales.