Light Intensity During Leaf Growth Affects Chlorophyll Concentration and CO 2 Assimilation of a Soybean Chlorophyll Mutant 1

An evaluation was made of leaf diffusive resistance and chlorophyll concentrations of dark green (normal) and pale green (chlorophyll deficient) phenotypes of a soybean [ Glycine max (L.) Merrill] mutant when grown 10‐ and 30‐klux light intensities. When grown at the 10‐klux intensity the two leaf types had similar mesophyll and total CO 2 diffusive resistances and similar net photosynthetic rates per unit leaf area at normal ambient CO 2 concentrations (e.g., 300 µl/liter). Chloropyhll concentration of the pale green leaf was one‐fourth that of the dark green leaf. On a chlorophyll basis, rate of CO 2 fixation was four times faster in the pale green type than in the dark green type. The similarity in net photosynthetic rates per unit leaf area of the two phenotypes when grown at the 10‐klux light intensity was the result of (1) similar CO 2 diffusive resistances and (2) the ability of the photosynthetic apparatus of the pale green leaf to fix CO 2 as rapidly as that of the dark green leaf, in spite of a much lower amount of chlorophyll. When grown at the 30‐klux light intensity, chlorophyll concentration of the pale green phenotype progressively declined, to one‐tenth the amount at the 10‐klux intensity. Chlorophyll concentration of the dark green phenotype was not significantly affected by light intensity. Photosynthesis of the pale green leaf grown at the 30‐klux intensity became CO 2 saturated at concentrations well below 300 µl/liter. Therefore, light intensity during leaf growth strongly influenced the relative CO 2 assimilation rates of the dark green and pale green phenotypes.