Saturation Deficit of the Mesophyll Evaporating Surfaces in a Desert Halophyte

The tensions developed in the internal evaporating leaf surfaces were estimated for a desert halophyte, Reaumuria hirtella, growing in its natural habitat. The method was based on the assumption that at zero transpiration the vapor pressure of the inner parts of the leaf was in equilibrium with that of the atmosphere, provided that stomatal resistance was constant during the measuring period. This could be ensured, since the measuring system controlled both the concentration of carbon dioxide and the atmospheric humidity, while measuring photosynthesis and transpiration simultaneously. Tension values of 180, 240, and 320 bars were recorded for three different Reaumuria hirtella plants.