Contribution of the adaxial and abaxial surfaces of olive leaves to photosynthesis

Abstract

Leaves of olive cultivars Frantoio and Maurino were irradiated with different irradiances from above, from below, or simultaneously from both directions to determine the contribution of the abaxial and adaxial leaf surfaces to photosynthesis. In both cultivars, irradiation of both sides of the leaf caused increases in net photosynthetic rate (P N) and apparent quantum yield compared to irradiating only one surface with the equal photosynthetic photon flux density (PPFD), but the PPFD needed to saturate P N decreased. At high and medium PPFD the P N determined at irradiating both leaf surfaces was less than the sum obtained at irradiation of only the upper or the lower surface with the same PPFD. At PPFD higher than 1000 µmol m-2 s-1 in cv. Frantoio and 1200 µmol m-2 s-1 in cv. Maurino, P N did not vary. At low PPFD (<200 µmol m-2 s-1), P N at irradiating the adaxial and abaxial leaf surfaces simultaneously was about the sum of the values obtained by irradiating the upper and lower surfaces separately. Consequently the compensation irradiance was reduced from about 50 µmol m-2 s-1 to about 30 µmol m-2 s-1 when irradiating both leaf surfaces. The natural leaf orientation of the olive cultivar influenced the utilization of radiant energy by the abaxial surface.