SOME ECOPHYSIOLOGICAL INDICATORS OF SALT STRESS IN GREENHOUSE TOMATO PLANTS

Tomato plants (cv Rondello) were grown in a multispan plastic greenhouse at two different salt concentrations in the nutrient solution, under high radiative and evaporative conditions of summer. After a week, we compared the behaviour of plants from the two treatments, with respect to leaf gas exchange parameters and sap flow through the stem.

The photosynthetic activity at ambient CO₂ (350 ppm) was reduced by 50% in salt stressed plants; the transpiration rate and stomatal conductance showed a reduction of 50% and 80% respectively.

At high CO₂ concentrations (>800 ppm) there was no significant difference in photosynthesis between treatments, giving evidence that in stressed plants the reduction was mainly due to stomatal limitation.

Sap flow through the stem very closely followed the changes in available radiation inside the greenhouse; but the values recorded on stressed plants were about 28% lower than in the control.

These preliminary results show that, also in field conditions, ecophysiological parameters can provide an explanation of plant response to stress. Nevertheless, considering the possible interaction between climatic factors, the evaluation of this response should be examinated also in relation to all growing conditions.