Effect of the Angle of Incidence of Light on the Net Photosynthesis Rates of Sorghum almum Leaves

Abstract

Modellers of plant canopy photosynthetic production make the assumption that there is no influence upon a leaf of the angle of incidence of parallel light it receives other than that arising from the geometrically reduced surface irradiance. This assumption was tested using attached leaves of Sorghum almum. Gas exchange measurements indicated that at oblique angles of incidence there was a marked reduction (up to 50% at 70°) in net photosynthesis rate below that expected on the basis of the reduced leaf surface irradiance. This 'angle effect' was shown to be at least partially the result of increased leaf reflectivity at oblique angles of incidence of light. The inclusion of this effect in a canopy model indicated that the common assumption tested could lead to a maximum overestimation of daily canopy production by about 7%.