The influence of certain environmental factors on diurnal and seasonal water stress patterns and their relationship to radial growth in mesquite, P̲r̲o̲s̲o̲p̲i̲s̲ g̲l̲a̲n̲d̲u̲l̲o̲s̲a̲ var. g̲l̲a̲n̲d̲u̲l̲o̲s̲a̲ Torr

Abstract

Water stress was measured in Mesquite, Prosopis glandulosa var. glandulosa Torr., using the pressure chamber method to detect negative hydrostatic pressures in the xylem of the leaf petiole. The method was shown to give a reliable measure of water stress under field conditions and to be sensitive to short term water stress changes. A potentially serious error in water stress (LWP) readings was minimized by making the measurements within 1 minute post-harvest. Diurnal patterns of water stress are dominated by factors of the aerial environment. Water stress (LWP) in mesquite has a curvilinear function with the vapor pressure deficit (VPD) of the atmosphere; however, the function is temperature and time of day dependent. The complexity of the regression model required to fit diurnal measurements of LWP to environmental variables suggests that an evaporative demand model of water stress is most complex and not fully acceptable. Indirect evidence suggests that complete reconciliation of LWP with environmental variables is dependent upon partitioning the heat load on the leaf between latent and convectional heat transfer. The seasonal trend of water stress in mesquite was measured throughout the 1968 growing season. An integrated value of daily water stress, termed net daily water stress, was found to be more sensitive to the seasonal influence of environmental factors than LWP measurements made at specific times during the day..