Agronomic and physiological aspects of salinity stress on a field-crown tomato crop

Horticultural plants in the Mediterranean ambient are often exposed to salt stress which causes limitation of stomatal and mesophyll CO2 conductance and reduces CO2 concentration in the leaf. Field-grown tomato plants (Lycopersicon esculentum, cv. Pachino) were grown in salt stress conditions by drip irrigating plant rows with water containing 1% (weight/volume) of commercial salt. Irrigation was given daily to restore the evapotranspirated losses. A replication was shaded with a white net to reduce by about 30% the incident solar radiation. Shading reduced the transpiration rate and, consequently, decreased the leaf and fruit sodium uptake in salt-treated plants. Because of the low salt uptake, leaf photosynthesis, stomatal and mesophyll conductance and Rubisco activity of shaded and salt-treated leaves was higher than in the non-shaded and salt-stressed leaves but still lower than in shaded or non-shaded controls. Shading may allow the use of water with moderate salt concentrations to irrigate tomato crops with limited and generally negligible consequences on plant physiology.