PHOTOSYNTHESIS, WATER RELATIONS AND GROWTH RESPONSES OF GREENHOUSE TOMATO PLANTS TO HIGH-SOLUTION ELECTRIC CONDUCTIVITY AND LOW SOIL WATER CONTENT: SOIL WATER DEFICIT ACCLIMATION AND SALT BUILD-UP EFFECT

Abstract

Greenhouse tomato plants (cv. Capello) were grown in peat moss based substrate and treated with high and low nutrient solution electric conductivity (EC) under high (95±5%) and low (55±8%) soil water conditions. Photosynthesis (Pn) was decreased about 25% 1 day after soil water content reached 55%. However, as the soil water deficit was prolonged, the effect of water deficit diminished, with the decreasing extent of ca 15% on the 11th and 16th days from starting treatments. This suggested that tomato plants acclimated to soil water deficit. One day after soil water content reached 55%, leaf turgor potential (TP) decreased largely as leaf water potential (WP) dropped. However, as soil water level was kept constant for a period, TP recovered to a quite large extent even at the same WP level. This TP recovery accounted for the photosynthetic recovery. Drying the constantly well watered plants to the same soil water level decreased Pn to a much larger extent than did the prolonged soil water deficit. This supports the above-mentioned photosynthetic acclimation. The effects of high EC were not observed 1 day after the treatments started, but became larger and larger as the treatments were prolonged. Build-up of EC in the soil accounted for this result