GROWTH, GAS-EXCHANGE AND ION CONTENT IN OLEA-EUROPAEA PLANTS DURING SALINITY STRESS AND SUBSEQUENT RELIEF

Olive (Olea europaea L, cv. Frantoio) plants grown hydroponically in a glasshouse were supplied with half-strength Hoagland solutions contai ning 0, 50, 100, and 200 mM NaCl for 4 weeks and subsequently supplied with the standard solution without NaCl to relieve salinity stress. T wo complete stress-relief cycles were repeated on the same plant mater ial during one growing season. Growth was inhibited at all salt levels , but most growth parameters of plants treated with 50 or 100 mM NaCl returned to control levels after 4 weeks of relief. More severely stre ssed plants (200 mM NaCl) recovered to only 60% of the growth of the c ontrols after 4 weeks. During relief, plants treated with 50 and 100 m M NaCl had net photosynthetic rates and stomatal conductances higher t han the controls. Increasing the NaCl concentration of the external so lution from 0 to 200 mM decreased both leaf pre-dawn water potential ( from -0.3 to -1.0 MPa) and osmotic potential (from -2.1 to -2.7 MPa). The sodium concentration in the leaves of plants treated with 200 mM N aCl reached maximum levels of 211 and 388 mM (expressed on a tissue wa ter basis) at the end of the first salinity and relief periods, respec tively. Leaf chloride concentrations were 359 and 223 mM at the same s ampling dates. These data indicate that the inhibitory effects of sali nization on growth and gas exchange of the salt-tolerant olive cv. Fra ntoio can be readily reversed when salinity is relieved, despite the m arked accumulation of potentially toxic ions (Na+, Cl-) in the leaf.