The Constructions And Applications Of The High-precision Sturctural Models Of Crop Canopy

The three dimensional (3D) plant structural modelling makes it possible to quantitatively simulate the interactions between the plant and environment.In this study, the high-precision 3D canopy models of maize and tobacco were constructed by measuring the surface morphologies of their leaves. However, the required computation time and computer resources will be very huge when these high-precision plant structure models were directly applied in relevant simulations such as the light intercepiton of the canopies. To overcome this problem, the high-precision leaf surface models were progressively simplified to evaluate the impacts of simplifications of leaf mesh and leaf undulations on the accuracy of the leaf-surface morphological descriptions, the plant architecture and light interception characteristics. Then, based on the canopy structural model, the light distribution model and the photosynthesis model, the optimization of the canopy architecture of field-grown tobacco was studied. The main contents are as follows:1. The leaf surface morphologies of field grown maize at the silking stage and tobacco after topping were measured using 3D laser scanning. High-precision leaf models were constructed based on the measurements, and were progressively simplified using two different methods-Vertex removal and Edge collapse. To evaluate the impacts of simplifications on the accuracy of the leaf-surface morphological descriptions, several error metrics were developed. These metrics are able to quantify these impacts in various respects. The statistical results show that most error metrics increase only marginally, even with moderate simplifications of the leaf surfaces. The errors, however, increase quickly with over-simplification. The simulation results of light distribution in these canopies indicate that over-simplifications of the leaf-surface meshes results in significant deviations in the simulated leaf light-capture efficiency compared with the original leaf surfaces. Compared with the Vertex removal method, the Edge collapse method is better at retaining the original leaf-surface morphology, but loses more of the leaf-edge information.2. Two types of simplified leaf surface models were constructed by progressively reducing the undulations of the scanned leaf model. The light interception of individual leaves and canopies constructed using the scanned and the simplified leaf surface models, were simulated using a 3D light distribution model. The effects of leaf undulations on the structural characteristics and light interceptions of the two crops were analysed at individual leaf and canopy scales. At the individual leaf scale, the changes of leaf architectural characteristics in leaf mesh simplification resulted in dramatically decrease of light-capture efficiency of individual leaves. For the more undulated tobacco leaves, the reduction of the light-capture efficiency could reach a maximum of 30%. At the canopy scale, leaf undulations gave rise to more deep penetration of the incident radiation into canopy, but only marginally improved the light condition at middle and lower canopy.3. Based on the 3D architectural model of tobacco canopy, different virtual experiments were conducted by adjusting the distances between plants and rows, row direction and leaf number of individual tobacco plants. The spatial distribution of Photosynthetically Active Radiation (PAR) and potential photosynthetic rate of virtual canopies under contrasting sky conditions were computed using a 3D light interception and photosynthesis model. The simulation results showed that the daily potential photosynthetic rate of the canopies increased till the row distance up to 110 cm or plant distance up to 60 cm. The largest PAR interception was reached when the row direction was around North-South direction (±20°). Removing two leaves at the top and two leaves at the bottom of each tobacco plant did not decrease the daily potential photosynthetic rate of the canopies, and this can improve the light condition of remained leaves of the canopy.