USE OF INTERACTIVE COMPUTER-GRAPHICS FOR SIMULATION OF RADIATION INTERCEPTION AND PHOTOSYNTHESIS FOR CANOPIES OF KIWIFRUIT VINES WITH HETEROGENEOUS SURFACE SHAPE AND LEAF-AREA DISTRIBUTION

A method incorporating interactive computer graphics to simulate spatially variable radiation interception and canopy photosynthesis is described. The method presents a graphical interface to a conventional model of radiation;interception and canopy photosynthesis. Included is the capacity to consider a large number of positions within the;canopy, thus providing a rapid and convenient representation of the dynamics of photosynthesis while also;overcoming limitations of one-dimensional models applied to complex plant canopies. The method was applied to;examine spatial variability of photosynthesis within canopies of kiwifruit;(Actinidia deliciosa);vines growing on two;trellis types. The diurnal integral of simulated canopy photosynthesis, assuming sunny conditions, for a vine trained;on a horizontal 2018;Pergola2019; trellis was 14% higher than that for a vine with similar leaf area distribution trained on;a 2018;T-bar2019; trellis with inclined surfaces. Simulations of photosynthesis for vines on a T-bar trellis, assuming spatially;variable leaf area distributions as measured under field conditions, indicated disproportionate contributions from;different regions of the canopy. Canopy regions inclined to the east or the west were usually the major sites for;photosynthesis immediately after sunrise and before sunset respectively, while regions near the cordon were the most;important overall. For any day, the maximum simulated photosynthetic rate generally declined with distance from;the cordon and, at any distance from the cordon, increased with leaf area index. For a vine with an average leaf area;index of 2-7, diurnal integrals of photosynthesis on a sunny day in late summer ranged from 10 mol C03;m-2;near;the cordon to O'5 mol C02;m-2;at F5 m from the cordon. Within-canopy shading was more important on sunny days;than on cloudy days, while the spatial distribution of leaf area was especially important on cloudy days. Comparison;of simulations with direct measurements of canopy photosynthesis indicated that a numerical integral of simulated;photosynthesis, based on a large number of canopy positions, provided a reasonable estimate of total canopy;photosynthesis. © 1993 Annals of Botany Company.