Gas-Exchange Properties of Salt-Stressed Olive (Olea europea L.) Leaves

The effects of two levels of salinity on photosynthetic properties of olive (Olea europea L.) leaves were observed either in low or in high H20 vapor pressure deficit (vpd). Under moderate salt stress, stomata were found to be less open and responsive both to light and vpd, but the predominant limitation of photosynthesis was due to the mesophyll capacity of CO2 fixation. We elaborate a procedure to correlate mesophyll capacity and liquid phase diffusive conductance. The estimated liquid phase diffusive conductance was reduced by salt and especially by high vpd; morphological and physiological changes could be responsible for this reduction. As a result, the chloroplast CO2 partial pressure was found to decrease both under salt and vpd stress, thus resulting in a ribulose-1,5-bisphosphate carboxylase limitation of assimilation. However, under combined salt and vpd stress, 02 sensitivity of assimilation increased, as would be expected under conditions of limiting ribulose 1,5-bisphosphate regeneration. Fluorescence induction measurements indicated that, under these conditions, energy supply may become limiting. When Cl- concentration exceeded 80 millimolar in tissue water, zero growth and 50% leaf drop was observed. Fluorescence induction showed irreversible damage at Clr levels higher than 200 millimolar and basal leaves reached this concentration earlier than the apical ones.