Research On The Effect Of Different Dwarf Rootstocks On Apple Canopy Structure And Photosynthetic Capacity Based On 3D Model

Canopy structure and photosynthetic capacity directly affect the formation of fruit yield and quality.As a major country in the production and consumption of apples,our country is currently in a critical period of transition from dense planting on vigorous stock to dense planting on dwarfing rootstock.There are differences in canopy structure and physiological processes of leaf photosynthesis and transpiration among different dwarfing rootstocks.Therefore,it is particularly important to select suitable dwarfing rootstocks.In this experiment,9-year-old Baleng+M9+Nagafu 2,Baleng+M26+Nagafu 2,M9+Nagafu 2 and M26+Nagafu 2 were used as test materials,and three-dimensional digital technology was used to combine the allometric growth of branches and leaves in order to establish three-dimensional virtual model of each dwarf rootstock canopy.Using the RATP functional structure model to simulate canopy photosynthetic productivity,combined with three-dimensional virtual experiments,the effects of different dwarf rootstocks on apple canopy structure,light interception,leaves and canopy photosynthetic productivity were systematically studied,with a view to optimizing canopy structure and screening Suitable rootstocks to provide reference.The main research results are as follows:（1）Combining 3D digital technology with allometric growth relationship of branches and leaves,virtual canopy model of apple was quickly established,and differences in canopy structure and spatial distribution of branches and leaves of different dwarf rootstocks were accurately evaluated and compared.（2）The canopy volume of M9+Nagafu 2 is small and the leaf porosity（P_o）is the highest,the leaf clumping index（μ）is low,and the leaf area density distribution in the canopy is more uniform,thus The light distribution in the canopy is improved,and the vegetative growth of the canopy is reduced.（3）In the isolated state,the overall canopy of M9+Nagafu 2 and the light interception value of each type of branch tip（STARi）are 0.33,0.29,0.39 and 0.26,respectively.Isolation,compared various treatments in the virtual orchard environment as a whole canopy and various（STAR_o）value decreased more than 40%,the topmost orchard plant spacing is too small,can reduce light interception efficiency,the actual production firm need to adjust depending on the type of different rootstock planting density,also showed that the construction of a virtual orchard can significantly improve the accuracy of evaluation of light interception.（4）The nitrogen content（N_a）per unit area of the leaves of Baleng+M26+Nagafu 2 and M9+Nagafu 2is the same as the daily cumulative amount of photosynthetically active radiation（PPFD_d）,and the maximum rate of carboxylation(V_Cmax),Maximum electron transfer efficiency(J_max)and Dark respiratory rate（R_d）linear relationship slopes are higher than that of Baleng+M9+Nagafu 2 and M26+Nagafu 2,respectively.The photosynthetic capacity of the leaves under the same N_a is stronger,and the light energy utilization efficiency is higher.The response curves of relative stomatal conductance to photosynthetically active radiation,temperature and saturated water vapor pressure（VPD）are similar,and the determination coefficients of each response model are large,and the simulation results are highly accurate.However,the optimized temperature and VPD critical value of Baleng+M26+Nagafu 2 and M26+Nagafu 2 are higher,indicating that their leaves are more resistant to high temperature and high VPD environments.（5）The relative stomatal conductance of each treatment showed an asymmetric bimodal curve to the daily changes of photosynthetic rate（P_n）,while the daily change of transpiration rate（T_r）showed a single-peak curve.Both Baleng+M26+Nagafu 2 and M9+Nagafu 2,the overall P_n and T_r of the canopy were significantly higher at each time during the day,indicating that the dry matter accumulation rate of the canopy was fast.The overall high P_n,T_r,total photosynthesis,total transpiration,and water use efficiency（WUE）of Baleng+M26+Nagafu 2 are 0.28 mol·m^-2·day^-1 and 79.33 mol·m^-2·day^-1,6.79 mol·day^-1,2000.34mol·day^-1 and 3.40 mmol·mol^-1,indicating that the canopy has a strong ability to accumulate dry matter.（6）The Baleng+M26+Nagafu 2 optimizes the fruit shape,significantly increases the sugar content of the fruit and reduces the acidity,and the M9+Nagafu 2 significantly increases the fruit weight per fruit.To sum up,it is suggested to establish a dense planting garden with dwarf rootstock in the Loess Plateau area by using Baleng+M26+Nagafu 2 and M9+Nagafu 2.