Study On Growth And Photosynthetic Characteristics Of Short-shooted Apple Tree Based On 3D Virtual Model

Apple canopy structure,light interception and canopy leaf photosynthesis all had important effects on apple quality and yield.Short-shooted type apple has been widely popularized because of its advantages of early fruiting,high yield and good economic benefits.Due to the difference of shoot composition and spatial distribution between short-shooted type variety and long-shooted variety,it will have an important impact on tree structure,light interception and function,but there is a lack of quantitative evaluation research.In this study,10-year-old spur-shooted type variety ’Liquan Fuji’ and long-shooted type variety ’Nagafu No.2’ are used as experimental materials.By combining the shoot code data,leaf morphological parameters and allometric growth relationship of shoots and leaves,the 3D virtual plant model was constructed,and the canopy structure,light interception and canopy photosynthesis of apples were systematically studied.The main findings are as follows:(1)The trunk cross-sectional area of‘Liquan Fuji’ is 79.41%of that of‘Nagafu No.2’,the interstock coarseness is 84.87%of that of ’Nagafu No.2’,and the average crown width is 90.81%of that of‘Nagafu No.2’.The trunk height,trunk cross-sectional area,interstock thickness and average crown width of ’Liquan Fuji’ are significantly smaller than those of’Nagafu No.2’.The result shows that the growth potential of spur-shooted type variety is obviously lower than that of long-shooted type variety.(2)The quantitative study on the tree structure of ’Liquan Fuji’ and ’Nagafu No.2’shows that the number of shoots per plant of the two varieties is approximately the same.From the point of view of shoot function,the number of vegetative short shoots of ’Liquan Fuji’ is 33.65%larger than that of ’Nagafu No.2’,and the number of bourse long shoots of’Liquan Fuji’ is only 50.20%of that of ’Nagafu No.2’.The number of vegetative short shoot of ’Liquan Fuji’ was significantly higher than that of ’Nagafu No.2’,and the number of bourse long shoots was significantly lower than that of ’Nagafu No.2’.From the point of view of shoot composition,the number of short shoots below 5cm of‘Liquan Fuji’accounted for 76.50%of the total number of shoots,and the number of short shoots below 5 cm of ’Nagafu No.2’ accounted for 56.58%of the total number of shoots.The results shows that the shoot composition and shoot function of spur-shooted type variety are more conducive to flowering and fruiting.(3)Based on the 3D virtual plant model,the light interception of the whole canopy and different types of ’Liquan Fuji’ and ’Nagafu No.2’ is quantitatively evaluated.From the point of view of the whole canopy,the total leaf area(TLA)of ’Liquan Fuji’ is 67.36%of that of’Nagafu No.2’,and the projected leaf area(PLA)is 71.12%of that of ’Nagafu No.2’.The TLA and PLA of ’Liquan Fuji’ are significantly smaller than those of ’Nagafu No.2’,but the canopy light interception(STAR)of ’Liquan Fuji’ was 0.02 larger than that of ’Nagafu No.2’.From the point of view of different types of shoots,the STAR of bourse short shoot of’Liquan Fuji’ is 26.32%larger than that of ’Nagafu No.2’,and the STAR of bourse long of’Liquan Fuji’ is 14.71%larger than that of ’Nagafu No.2’.The results shows that the light distribution and light interception efficiency of the whole canopy and fruit shoots of spur-shooted type are better than that of long-shooted type.(4)The diurnal changes of net photosynthetic rate(Pn),stomatal conductance(Gs)and transpiration rate(Tr)of ’Liquan Fuji’ leaves and ’Nagafu No.2’ leaves showed a unimodal curve.The daily average net photosynthetic rate of’Liquan Fuji’ leaves was 13.05%larger than that of ’Nagafu No.2’ leaves,the daily average stomatal conductance was 25%larger than that of ’Nagafu No.2’ leaves,and the daily average transpiration rate was 17.34%higher than that of ’Nagafu No.2’ leaves.The light saturation point(LSP),light compensation point(LCP),maximum net photosynthetic rate(Amax),maximum carboxylation rate(Vcmax)and maximum electron transfer rate(Jmax)of ’Liquan Fuji’ sun leaves and shade leaves are higher than those of ’Nagafu No.2’ sun leaves and shade leaves,respectively.The optimum temperature of sun leaves of the two varietiesis is 30℃ and that of shade leaves of the two varietiesis is 28℃.Sun leaves and shade leaves of ’Liquan Fuji’are in better condition at low VPD.The optimum VPD of sun leaves of ’Nagafu No.2’ is 2.0 kPa and the optimum VPD of shade leaves of ’Nagafu No.2’ is 1.6 kPa.The results shows that spur-shooted type leaves have better stress resistance at high temperature and high VPD.Compared with long-shooted type variety,spur-shooted type variety has stronger photosynthetic capacity in single leaf.(5)There is only a significant difference in fruit coloring between spur-shooted type variety and long-shooted type variety,but no significant difference in single fruit weight,fruit shape index,fruit hardness,soluble solids and titratable acid content.The number of fruits per plant of ’Liquan Fuji’ is 69.53%of that of ’Nagafu No.2’,and the yield per plant of’Liquan Fuji’ is 71.68%of that of ’Nagafu No.2’.There is no significant difference in the yield per cross-sectional area of trunk between the two varieties.