THE EFFECT OF NACL STRESS AND RELIEF ON GAS-EXCHANGE PROPERTIES OF 2 OLIVE CULTIVARS DIFFERING IN TOLERANCE TO SALINITY

Young olive plants (Olea europaea L.) were grown either in hydroponic or soil culture in a glasshouse over two growing seasons. Plants were exposed to NaCl concentrations between 0 and 200 mM for 34-35 days fol lowed by 30-34 days of relief from stress to determine the effect of s alinity on gas exchange of two cultivars ('Frantoio' and 'Leccino') di ffering in salt-exclusion capacity. Salinity stress brought about a re duction in net CO2 assimilation and stomatal conductance in both culti vars, but the effect was more pronounced in the salt tolerant 'Frantoi o' than in the salt-sensitive 'Leccino' cultivar. Therefore, gas excha nge parameters may be misleading if used to evaluate the salt toleranc e of olive genotypes. Recovery in gas exchange parameters during relie f from stress was slower in the salt sensitive cultivar. In general, t he decline in assimilation reflected the salt-induced reduction in sto matal conductance, but a marked effect on carboxylation efficiency and CO2 compensation point was measured in plants treated with 200 mM NaC l for four weeks. The cultivar 'Frantoio' showed a 50% reduction in as similation and stomatal conductance at 146 and 78 mM leaf Na+ concentr ation (tissue water molar basis) respectively, whereas the correspondi ng 50% thresholds for the cultivar 'Leccino' were at 275 and 264 mM, r espectively.