Water stress, water use efficiency, carbon isotope discrimination and leaf gas exchange relationships of the bush bean

Water use efficiencies for the whole plant (WUEt) and single leaves (WUEi) were studied in a greenhouse as a function of soil moisture during four phenological stages of bush bean growth. WUEt increased significantly with soil moisture stress and attained its maximum value before the flowering stage. WUEt and WUEi were linearly related (r = 0.92), and WUEi was correlated with the transpiration rate (r=-0.87), stomatal conductance (r = -0.80) and photosynthetic rate (r = 0.81). Carbon isotope discrimination,), decreased as soil moisture decreased, and ) was negatively correlated with both WUEt (r = -0.92) and WUEi (r = -0.88). There were significant differences in leaf N among water regimes.