Interactions among leaf photosynthetic rates, flowering and pod set in soybeans.

The seasonal maximum in photosynthetic CO2 exchange rate (CER) and the cessation of leaf expansion in soybeans (Glycine max (L.) Merr) accompany fruiting under normal agricultural conditions. To investigate whether these phenomena were obligatively tied together, we caused early flowering of long-season varieties by imposing artificial short-day treatments. Comparisons of CER and leaf area between vegetative (long-day treatment) and fruiting (short-day treatment) plants of long-season cultivar confirmed the relationship of these phenomena. The same comparisons made between a long-season and a short-season cultivar, both at the same daylength, also confirmed the relationship.