Photosynthesis of crop plants as influenced by light, carbon dioxide, temperature, and stomatal diffusion resistance

Abstract

The effect was estimated of light intensity, leaf temperature, and C0 2 concentration on photosynthetic rate in leaves of crop plants. The potential capacities of photochemical and biochemical processes and of C0 2 transport were compared.Resistance to C0 2 transport in various parts of the pathway from external air to reaction centre in the chloroplasts was estimated in absolute units. This allowed quantitative comparison of micrometeorological and physiological effects on photosynthesis.C0 2 transport towards the leaf is affected by the sum of resistances in external air (r a ), stomata (r s ), and mesophyll cells (r m ). Since r m is usually larger than r s of open stomata, r m is probably an important yield determining factor.With adequate water-supply, transpiration depends on r s + r a , but not on r m . Therefore higher values of r s and lower values of r m favour the water balance of crops.With strong light and leaf temperature around 22°C, C0 2 saturation of photosynthesis was reached with C0 2 concentrations between 01 and 0.15 %.Techniques were described for accurate measurement of C0 2 and water vapour, leaf temperature, light intensity and diffusion resistance. The importance of different types of light bulbs for photosynthesis was evaluated, and much attention was paid to accurate assessment of effective C0 2 concentration in the air around leaves in assimilation chambers.