Leaf Morphology and Anatomy in Relation to CO2‐exchange Rate of Soybean Leaves¹

Abstract

To learn more about factors limiting leaf photosynthesis of soybeans [ Glyclne max (L.) Merr.], we examined the relationships among leaf morphological and anatomical characteristics and CO 2 ‐exchange rate (CER). Infrared gas analysis of the most recent, fully expanded, attached leaf of outdoor, pot‐cultured plants was measured in the laboratory under saturating irradiance, after which stomatal impressions were taken and leaf sections were prepared for anatomical measurements Specific leaf weight (SLW), which seemed a function of thickness and not deusity, and leaf thickness (LT), itself, were correlated with CER. The thickness differeuces were most strongly expressed in the upper palisade and paraveinal mesophyll layers. Vapor phase diffusion resistance to CO 2 accounted for 22 and 13% of the variation in CER in each of 2 years, and only in the former year, when aperature on the adaxial surface was strongly correlated with resistance and CER, were stomatal characteristics related to CER. Residual (mesophyll, carboxylation) resistance accounted for 15 and 53% of the variation in CER the 2 years. Both CER and residual resistance were related to the thickness and cellular volume of the several leaf tissue layers, but they were poorly related to cell diameters, exposed cell surface area, and cell surface to volmne ratio. We conclude that characteristics internal to the cell, as opposed to resistances related to stomata, intercellular space, or cell surfaces, were regulating CER in these soybean leaves.