20 - Environmental and Developmental Effects on Carbon Isotope Discrimination by Two Species of Phaseolus

Abstract

This chapter discusses the effects of environment and plant developmental status on carbon isotope discrimination by two species of Phaseolus. Common bean—Phaseolus vulgaris L.—is the most important of the five cultivated species in the genus Phaseolus. Phaseolus vulgaris is drought-sensitive and yields are reduced by mild water stress. By contrast, tepary bean—P. acutifolius A. Gray—is native to the southwestern United States and northern Mexico, is adapted to heat and drought stress, and out-yields P. vulgaris under hot and dry conditions. To understand the ecophysiological characteristics of these two species, the study discussed in the chapter compares carbon isotope discrimination by P. vulgaris and P. acutifolius in response to environmental variation, plant developmental status, and their interactions. P. vulgaris L. and P. acutifolius Gray were grown in the field at two levels of soil moisture and two levels of soil nitrogen to evaluate environmental and developmental effects on carbon isotope discrimination (Δ) and water-use efficiency (A/E). Leaf Δ values were significantly lower for P. acutifolius than for P. vulgaris in all experimental treatment combinations.