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 'Pergola' trellis was 14% higher than that for a vine with similar leaf area distribution trained on a 'T-bar' 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 1.0 mol CO2 m-2 near the cordon to 0.5 mol CO2 m-2 at 1.5 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.