A procedural approach for studying the radiation regime of infinite and truncated foliage spaces. Part III. Effect of leaf size and inclination distribution on nonparallel beam radiation penetration and canopy photosynthesis

Abstract

The procedural approach was used to study the effect of leaf size and inclination distribution on nonparallel beam radiation penetration and canopy photosynthesis. Horizontally infinite stands at two leaf sizes (leaf area = 0.0051 and 0.0813 m 2), were generated in the computer. Five model leaf-inclination distributions were chosen; uniform, planophile, erectophile and distributions in which the leaf angle is either 0 or 90° at the top of the canopy (Models III and IV, respectively) and changes to the other extreme towards the bottom in relation to cumulative leaf area index. Erect-leaved canopies were found not only to allow relatively more radiation to reach the lower layers but also markedly affect its distribution, primarily by having a higher proportion of penumbral solar irradiance. Model IV canopy has the highest photosynthetic rate compared with other canopies; in this type of canopy (smaller leaf size), the effect of leaf inclination distribution on momentary photosynthetic rates is as high as 86%. A quantitative evaluation of the degree of discrepancy between parallel and nonparallel radiation penetration and consequently canopy photosynthesis in relation to stand architecture is given.