Transpiration, Stomatal Conductance, and Photosynthesis of Tomato Plants with Various Proportions of Root System Supplied with Water1

Abstract

Tomato ( Lycopersicon esculentum Mill.) plants were grown in specially designed sectional treatment boxes which divided the root systems into 4 separate quadrants. Transpiration, photosynthesis, and stomatal conductance were determined in tomato plants with 4, 3, 2 and 1 quadrants of the root system supplied with water. The results suggested that there was no simple relationship between the percentage of root available for water uptake and transpiration rate. The shoot: root ratio of tomato plants increased as the proportions of roots supplied with water increased. The application of water to only 50% or 75% of the root system did not reduce transpiration, photosynthesis, stomatal conductance, or leaf surface area compared to a fully-watered plant. Where a substantial part of the root system (75%) was subject to moisture stress, only a small reduction in transpiration rate (20%) was observed. These results suggested that tomato roots had a greater relative absorption capacity for water uptake in response to the transpirational demand. The recovery of transpiration, photosynthesis, and stomatal conductance following the return to a fully watered state indicated that there had been no damage to the roots in the dry quadrants in any of the treatments.