Distribution Simulation Of Photosynthetically Active Radiation And Light Interception Ability Analysis Within Loquat Canopy

Photosynthetically active radiation(PAR)is the main energy source of plant photosynthesis.The morphological structure of the plant canopy determines its internal light distribution,thus affecting the light interception ability and the microenvironment within the canopy,which largely influences the plant's growth and development process.The traditional method of studying light distribution within canopy through field measurement is time-consuming and labor-consuming,lacking of the guarantee of the space-time resolution.Using computer simulation and analysis method is one of the effective ways to overcome this probilem.In this paper,taking loquat tree as an example,virtual plant technology was used to quantitatively simulate and analyze the light distribution within canopy and light interception ability.The main research contents and results are as follows:(1)According to the field survey and literature data,obtain the morphological structural parameters of loquats,and then use L-system modeling method to compile the L-system rules,finally establish a three-dimensional model of the trunk system.Use a hand-held structured light scanner to obtain point cloud data of the canopy leaf organ and establish a three-dimensional model of the leaf organ.Integrated the leaf organ model and the trunk system model,forming a fine three-dimensional individual loquat tree model.(2)Based on the extended radiation model,the distribution of solar direct PAR and sky diffuse PAR within individual loquat canopy are simulated respectively.Under the two different light conditions,make a quantitative analysis of the spatial distribution of PAR within canopy at different moments during daytime to draw some conclusions.The light is mainly distributed on the periphery and in the middle and upper area,and the inner area and middle and lower layers within canopy are covered seriously by foliage and branches.The radiant energy received by the canopy shows a single peak change over time,with the strongest solar radiation at noon and the weakest on the morning and evening.Besides,the scheme combining the simulation of PAR within the canopy and the field verification is proposed to verify the accuracy of the simulation result by contrasting the computer simulation process with the measured data of the radiation sensors.(3)Based on the simulation results,in terms of the area of leaves receiving light and the energy of leaves receiving radiation,choose these light interception analysis indicators respectively,i.e.silhouette to total area ratio(STAR)and relative photosynthetically active radiation(RPAR),to study the spatial distribution of light interception and it diurnal trend from sunrise to sunset.The results show that light within canopy is mainly distributed in the periphery and upper and middle regions by the sunlight side,while the inner and lower regions by the shay side show low light interception efficiency.(4)Simulate the diurnal variation of STAR,RPAR and net photosynthetic rate within canopy of several crown-shaped loquats,analyze the effects of crown shape on canopy light interception ability and Pn through comparison.The results show that the light interception ability varies obviously among different crown-shaped loquats.The loquat with open-center canopy owns the maximum Pn and the highest light interception efficiency,which proves its crown structure is more reasonable.Quantitatively analyze the light distribution within canopy and explore the influence of the canopy structure on light interception,which can provide reference for pruning and ideal plant crown design.