Leaf Anatomy of Soybean [Glycine Max. (L.) Merr.] In Relation to Gas Exchange and Dry Matter Productivity.

Soybean [Glycine max. (L.) Merr.] is an important oil and protein crop. The yielding ability and its physiological basis, especially for leaf gas exchange, were examined for various soybean cultivars. In the field experiment, US soybean genotypes exhibited greater seed yield for 16% and 39% compared with Japanese genotypes on average in 2008 and 2009, respectively. These differences were mainly explained by the genotypic variation in dry matter productivity and radiation use efficiency (RUE). The theoretical potential of gas exchange capacity of single leaf (g_p) was defined by the leaf epidermal structure. Among various varieties, g_p was also greater in US varieties compared with Japanese varieties for 29% and 21% on average in 2008 and 2009, respectively. The positive correlation was observed between g_p and stomatal conductance (g_s) measured under the field condition. The genotypic differences in g_s were fairly stable throughout the daytime on clear sunny day. These findings suggest that greater gas exchange, sustained by leaf epidermal structure, contributes to the greater RUE and seed yield in US varieties. The variation of g_p was totally explained by stomatal density, suggesting the importance of this trait on leaf gas exchange. The clear correlation in genotypic variation of stomatal density between two years (r = 0.84**) encourages the effective screening of this trait, and hence the indirect selection of leaf gas exchange capacity in future breeding of soybean. The large and continuous variation was observed in stomatal density among recombinant population between an US and a Japanese variety, which suggest the multi-gene regulation on this trait. The genetic analysis on the variation of stomatal density, as well as the evaluation of the significance of this trait to dry matter productivity, may accelerate the genetic optimization of leaf gas exchange and dry matter productivity in soybean.