Movements of the Trifoliate Leaf of Bean ( Phaseolus vulgaris L.) during a Simulated Day, and their Consequences for Solar-Tracking Fidelity and Interception of Solar Radiation

Abstract

Summary Movements of the terminal and lateral leaflets in the trifoliate leaf of pinto bean (Phaseolus vulgaris L.) cv. Bulgarian were studied under simulated daytime conditions (12-h photoperiod), during which a light source directed on the leaflet lamina was moved at the angular velocity of the earth (15 deg h-1) in a vertical arc centered on the pulvinule, either along the plane of the mid-vein, or transversely, at right angles to it. The time-course of change in laminar elevation, azimuth and rotation was recorded. These data were used to evaluate the fidelity of solar-tracking and calculate the changes of laminar orientation to the sun (angle of light incidence, AI) throughout the day. Interception of incident light throughout the day was estimated by the ratio between the PPF incident on the lamina and on a perpendicular surface, and was calculated as cosine of the angle of light incidence on the lamina. Leaflet movements contributed to the interception of solar radiation, but did not exhibit significant, or consistent solar-tracking. Calculated integrated interception by all three leaflets was similar in all directions of solar traverse over the trifoliate leaf.