WATER-STRESS, WATER-USE EFFICIENCY, CARBON-ISOTOPE DISCRIMINATION ANDLEAF GAS-EXCHANGE RELATIONSHIPS OF THE BUSH BEAN

Water use efficiencies for the whole plant (WUEt) and single leaves (W UEi) were studied in a greenhouse as a function of soil moisture durin g four phenological stages of bush bean growth. WUEt increased signifi cantly 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), stomata l conductance (r = -0.80) and photosynthetic rate (r = 0.81). Carbon i sotope discrimination,), decreased as soil moisture decreased, and ) w as negatively correlated with both WUEt (r = -0.92) and WUEi (r = -0.8 8). There were significant differences in leaf N among water regimes.