基于虚拟植物的枇杷冠层光环境模拟与分析

As one of the most important resourses for plant photosynthesis, light is a key ecological factor affecting the fruit tree growth, development, fruit yield and quality. The canopy structure determines the light interception and distribution. Using loquat as study object, We will systematically analyze a number of loquat canopy structure and find out structural development law.The plant modeling method will combined partial digitizing of tree structure with reconstruction rules for non-digitized organs. Several detailed three-dimensional(3D) canopy models will be constructed, which would show loquat canopy characteristics at different growth stages and growing seasons.The light interception and distribution within canopy on organ level will be simulated based on the physical process of light transmission.The simulation consists of an architecturally accurate virtual plant coupled with 3D light transfer models and a leaf photosythesis module. Different scenarios of local light interception and distribution, incident light and photosynthesis will be modelled and calculated within the canopy in order to explore the reasonable canopy shape for procuction planting. The spatial and temporal distribution patterns of soalr radiation within the canopy can help undersatnd the relationships between solar radiation and and fruit diseases,and clarify the light environment how to affect fruit quality.In order to explore a sound orchard cultivation and management method with improved light use efficiency, scenarios of different tree plantation density, direction of row planting and pruning intensity will be constructed, the light environment within orchard will be simulated and analyszed accordingly. The main objective of this research is to provide a novel useful tool for quantitative analysis of canopy structure and pruning effect. The research result will be helpful for explaining loquat diseases mechanism and finding out reasonable preventive measures, as well as providing theoretical basis for orchard production capacity forecast, orchard population structure adjustment, etc. on precision agriculture management measures.

光是植物光合作用最基础的资源，是影响果树生长、发育和果实产量、品质的重要生态因子。果树冠层形态结构决定着对光的截获和分布。本项目以枇杷为对象，分析冠层的形态结构特征和生长发育规律，旨在通过冠层局部精细几何建模与植物规则建模相结合，建立不同树龄不同物候期的枇杷精细三维模型。模拟冠层内光辐射传输过程，计算器官尺度上的辐射强度；结合光合作用模型，分析各种不同冠形的枇杷对光的截获能力和净光合速率，探索对生产有指导意义的科学合理冠形；研究冠层各部位光辐射时空变化规律，揭示光辐射与果实病害之间的定量关系，阐明光环境对果实品质的影响。按照不同种植密度、行植方向、整形修剪方法、模拟不同生境的三维果园和光环境，定量分析果园群体对光的利用率，探索合理的、高光效的果园栽培管理方法。研究成果将为冠形分析提供定量分析新方法，为果树生产能力预测、果园群体结构调整等精细农业管理措施提供理论依据。

果树形态结构决定冠层内的光分布，从而影响光合作用和冠层微环境，影响果树生长、发育和果实产量、品质。植物生长周期长、形态结构复杂，田间实验难，且费时费力。针对该问题，提出基于虚拟植物的冠形设计、光截获能力分析的方法。主要研究内容和成果如下：.（1）提出规则和点云数据综合驱动的单树精细建模方法，把树木分成主体枝干系统和冠层局部组分分别建模。基于L-系统规则生成主体枝干系统三维模型；基于点云数据生成精细的冠层局部组分的三维模型；根据拓扑关系进行集成，生成整株木的三维模型。在已有单树建模软件LSTree基础上，研发交互修剪模块，提供虚拟修剪的软件工具。.（2）集成精细的三维冠层模型和辐射度算法，利用GPU对辐射度算法的形状因子求解并行化，提高算法的效率，研发了植物冠层内辐射传输过程模拟模块，模拟冠层内光分布，可计算辐射冠内的每个面元获得的光合有效辐射（PAR）的量。.（3）交互调整分支角、枝梢数、长短枝比例等参数，形成不同的冠层模型，从冠层轮廓区域面积比例、净光合速率、无效光区等方面分析枝条和冠层尺度的光截获能力，设计高光效的株型。结果表明枇杷分支角对光截获有显著的影响，当单枝的2级枝条与枝干间夹角约为15°时和整株2级枝条间夹角为60°-90°时，光分布比较合理。.（4）建立了不同地形条件和种植方案的虚拟枇杷果园，模拟了不同种植密度、不同地形坡度与不同地形坡向条件下虚拟枇杷果园冠层内PAR分布，分析各种情景下枇杷果园冠层对光的利用率。果园冠层截获的地面反射PAR能量主要作用于冠层内部与下层。.（5）根据田间测量数据分析得出，紧凑型枇杷叶片净光合速率最高，矮化疏枝型枇杷和矮化开张型枇杷净光合速率差异不大；紧凑型枇杷的蒸腾速率和气孔导度最高，矮化开张型枇杷居中，矮化疏枝型枇杷最低。胞间CO₂浓度表现为，紧凑型的胞间CO₂浓度最高，矮化疏枝型次之，矮化开张型最低。表明紧凑型枇杷的光合作用特性较高，矮化开张型枇杷居中，矮化疏枝型枇杷较低。