Variation in nectar characteristics within soyabean cultivars

Variation in floral nectar characteristics within soyabean (Glycille max (L.) Merr.) cultivars Centennial and Coker 237 grown in Marion, Arkansas, USA was examined in 1980 and 1981. Nectar characteristics (nectar per flower; fructose, glucose, and sucrose contents; total nectar carbohydrate content; and total carbohydrate per flower) within cultivars varied significantly among days, and over time and with temperature within days. Environmentally induced differences in specific nectar carbohydrate composition were observed between years; water deficiency in 1980 promoted a decrease in sucrose content and an increase in fructose and glucose content. In 1980 fructose and glucose contents varied from about 200 to 300 ml; in 1981 they varied from only about 25 to 125 mg/ml. Sucrose was not detectable in many morning samples in 1980; however, concentrations in afternoon samples were similar to those observed in 1981. The potential significance of the observed variance in nectar characteristics on honeybee (Apis mellifera) foraging is discussed.