Leaf Photosynthetic Characteristics of Determinate Soybean Cultivars1

Abstract

Apparent photosynthesis (AP), photorespiration (Pr), transpiration (T), specific leaf weight (SLW), and diffusion resistances were measured to characterize these physiological parameters in 16 determinate soybean [Glycine max (L.) Merr.] cultivars, four each in maturity groups V through VIII. Data were obtained on 12 to 16‐day‐old terminal leaflets attached to plants grown in a greenhouse.In three separate sets of measurements AP rates of the 16 cultivars ranged from 23 to 37 mg CO₂ dm⁻² hour⁻¹ and differences among cultivars were found in each of the three measurements. Significant differences among cultivars were also observed in Pr, T, and SLW. Mesophyll diffusion resistance (r_m) calculated from AP and T data also differed among cultivars. Pr not only increased as AP increased but also accounted for a higher percentage of photosynthesis in cultivars with higher Pr. AP rate was positively correlated with T and negatively correlated with laminar plus stomatal (r_a+r_a) diffusion resistance and with r_m. The correlation of AP with SLW was significant in only one of three measurements. The determinate cultivars examined in this study display for most physiological parameters a similar range in cultivar performance as published reports for indeterminate cultivars.