The influence of axial rotation upon interception of solar radiation by plant leaves

Abstract

Axial rotation of a plant leaf about the midrib is an important factor which permits effective maximization or minimization of the interception of direct solar radiation. Through use of matrix rotations of coordinate systems, the cosine of the angle of incidence, a measure of the fraction of solar radiation intercepted by the leaf, is described as a function of angles which specify the relative orientation of the leaf to the sun. All of these angles can be measured directly except for the axial rotation angle, which may be calculated from more easily measured quantities. Computer modeling and theoretical calculations demonstrate that relatively large amounts of average axial rotation permit a plant to reduce the cosine of angle of incidence of each flat leaf to zero, resulting in no interception of direct solar radiation, while smaller amounts of average axial rotation allow a plant to intercept as much as 80% of direct radiation, even if leaves are distributed uniformly over 360° of azimuth.