Predawn water potential equilibrium of leaves in common bean under soil water deficit

Abstract

The objective of the present study was to determine whether a predawn water potential equilibrium could be reached in all leaves of bean (Phaseolus vulgaris L.) under soil water deficit. The plants were grown in a greenhouse in pots with sandy-silt soil. These pots were subjected to withholding-watering (WW) and normal watering (NW) treatments. Predawn leaf water potential (ψlp) in leaves of the main stem, evapotranspiration and transpiration, stomatal conductance, progress of the permanent wilting condition (PWC) of leaves at different levels of the main stem, soil water percentage and vapor pressure deficit (VPD) were registered. Leaf water potential equilibrium among leaves was reached at predawn (from 4:30 to 6:30 h) in WW and NW, notwithstanding some degree of evapotranspiration, transpiration, stomatal conductance and VPD during the night period. The ψlp was highly influenced by soil water content. Since a close relationship was found between ψlp and soil water content, ψlp might be employed as an indicator of the soil water availability. In WW, when the Ylp was reduced from -0.5 to -1.1 MPa, the rates of evapotranspiration and transpiration were minimum, indicating the onset of deficit of available soil water. The experiment was ended the date of the onset of the PWC of the third compound leaf which coincided with the value -1.5 MPa of the ψlp. Thus, ψlp is a good quantitative parameter for evaluating the accumulated water stress of the plant.