Physiological mechanisms of adaptation of vegetative fig plants to salinity

Experiments on the response of young fig (Ficus carica L. ‘Dottato’) plants to saline water were conducted over two years. The typical experiment consisted in irrigating container-grown plants with pure (control) or saline water at 50, 100 or 200 mM NaCl concentrations for 7-8 weeks in a glasshouse. Plant water status and leaf gas exchange were measured at 10-15 d intervals, dry matter distribution in different organs was determined at the end of the experimental period. Young fig plants tolerated well salinity concentrations up to 100 mM NaCl. Shoot growth and leaf expansion slowed down in 100 mM NaCl-salinized plants, but foliage remained healthy and toxicity symptoms appeared only at NaCl concentrations higher than 100 mM. It took between two to three weeks before relative water content and net photosynthetic rate of fig leaves were significantly reduced by salinity compared with control plants. The stem dry weight was significantly lower than the controls only for the 200 mM-treated plants, whereas that of leaf and root tissues was lower also for the 100 mM NaCl treatment. The ratio between above and below ground dry matter did not vary significantly across the 0-100 mM NaCl range, whereas it was significantly lower for the 200 mM NaCl plants. Fig trees are suitable for cultivation in saline areas provided that the NaCl concentration of the irrigation water does not exceed 100 mM.