Water relations of cork-oak (Quercus suber L.) under natural conditions

Abstract

Daily and annual courses of leaf transpiration, stomatal conductance and shoot water potential of four Quercus suber individuals were compared in a semi-natural stand in southwest Portugal, from spring 1989 to early summer 1990. The trees investigated showed annual patterns typical of evergreen sclerophyllous species but varied in their range of stomatal operation. This appeared to be related to differences in hydraulic conductivity in the root-to-leaf pathway. Maximum stomatal conductance and transpiration rates occurred from March to June. Water stress was found to be moderate and winter cold stress due to low air and soil temperatures appeared to have an influence on plant water balance through their effects on flow resistances. Abbreviations." gsw stomatal conductance; gmax maximum stomatal conductance, PAR, photosynthetically active radiation; RH, relative humidity of the air; T, leaf transpiration; Ta, air temperature; TL, leaf temperature; Tmax maximum leaf transpiration; ∆W, air-to-leaf vapor pressure difference; W, shoot water potential; ψPD, predawn shoot water potential; ψMIN, minimum shoot water potential.