Effect of light on gas exchange parameters of sun and shade adapted leaves of Ceratonia siliqua, Coffea arabica and Malus domestica

Abstract

Wong et al. (1978, 1979) hypothesized that leaf photosynthesis and stomatal conductance are regulated in such a manner that Ci remains fairly constant despite changes in environmental conditions (see Beyschlag et al. in this volume). Nevertheless, studies in which carbon dioxide in the external air (Ca) and consequently carbon dioxide concentration in the mesophyll intercellular spaces (Ci) are varied, help determine the manner in which mesophyll photosynthetic activity, in large part determined by ribulose bisphosphate carboxylase activity, affects photosynthetic CO₂ uptake. While measurements of Ci are critical, only indirect methods are available to accomplish them, and it is controversial whether the molar concentration of carbon in solution (Ku and Edwards 1977) or the equilibrium partial pressure in the air space is the appropriate measure of CO₂ available for photosynthesis. In the present work, changes in photosynthetic activity of the leaf mesophyll were related to Ci, calculated from stomatal diffusion resistance, the rate of net photosynthetic CO₂ flux and Ca (using volume fraction as concentration units, µl 1⁻¹).