Elevation and transpiration: some theoretical considerations with special reference to Mediterranean-type climate.
Under isothermal conditions the decrease in air pressure with elevation enhanced potential transpiration by increasing the leaf to air water vapour gradient and by increasing the diffusivity of water vapour in air. This change was modified in both degree and direction by the character of the temperature lapse rate. Under isothermal and especially under temperature inversion conditions, the lower barometric pressure and increased solar radiation flux associated with increasing height combined to produce very high rates of potential transpiration. When temperature fell with height at rates approaching the average mid-latitudinal lapse rate (-0.0065 deg C/m), air temperature became the dominant factor and transpiration fell with increasing height. Stomatal closure in response to high rates of potential transpiration reduced growth and contributed to the development of xeromorphism.