WATER RELATIONS OF LEAVES OF SONIA ROSE PLANTS GROWN IN SOILLESS GREENHOUSE CONDITIONS

Rose plants (Rosa hybrida cv. Sonia) were grown in rockwool in two heated greenhouses: one with relative humidity (RH) control (RH >70%) provided by high-pressure mist, the other protected against overheating using a movable screen without RH control. Two electrical conductivity (EC) rates were applied: high (EC of drainage water almost-equal-to 3.8 mS.cm-1) and low (EC of drainage water almost-equal-to 1.8 mS.cm-1). Under these conditions, water deficit in plants was due mainly to climate, and not to EC. The relative water content of sample leaves picked at noon (RWC(noon)) was one to two percentage points higher in the greenhouse with RH control and dropped by 6% to 7% in summer. RWC(noon) was unaffected by differences in EC. The average elastic modulus (epsilon) and the relative water content threshold for turgor loss (RWC0) were reduced in the greenhouse with RH control. epsilon was increased in the high EC treatment, but RWC0 remained unaffected.