Variability of Leaf Morphology and Stomatal Conductance in Soybean [Glycine max (L.) Merr.] Cultivars

Leaf epidermal structure is an important determinant of leaf gas exchange in soybeans [Glycine max (L.) Merr.] and can be used as an indirect criterion for the selection of gas exchange traits. The objective of this study was to assess the genetic variation of leaf morphology among soybean cultivars and to examine how U.S. and Japanese cultivars differ with respect to gas exchange. Over 70 cultivars, including U.S. and Japanese soybean, were grown in the field over 2 yr to determine stomatal density, guard cell length, and potential stomatal conductance, along with other morphological leaf traits. Among cultivars, stomatal density ranged from 148 to 334 mm−2 Large variation was found in potential stomatal conductance (gp), which was closely associated with stomatal conductance in the field for representative genotypes (r = 0.89, P < 0.01). United States cultivars had larger gp values than Japanese and other Asian cultivars. This potential may give a physiological and morphological basis for the greater productivity observed in U.S. cultivars. On the other hand, PI 416937 showed lower stomatal conductance, which is consistent with the ability to conserve water. This study indicates the importance of leaf structure in determining gas exchange and suggests that these characteristics may be optimized to enhance dry matter productivity and water use.