Measurement of Total and Osmotic Potentials in Lucerne and Sunflower Tissues using Thermocouple Psychrometers

Abstract

SummaryThe measurement of leaf water and osmotic potential using thermocouple psychrometry was investigated in field grown stands of sunflower and lucerne. For the chamber size and tissue dimensions used, vapour pressure equilibrium was achieved after 4 to 6 h for leaf water and osmotic potential samples. In lucerne, as the time delay between excising the leaf and sealing it in the chamber was increased from 30 s to 8 min, water apparently evaporated from the leaf sample and leaf water and osmotic potential markedly decreased. For routine psychrometer determinations of leaf water and osmotic potential in lucerne (and presumably other species) leaf samples should therefore be sealed in the chambers as quickly as possible to minimize rapid water loss and associated errors in water potential determination. Vapour pressure equilibration for sunflower capitulum and root water and osmotic potential samples was achieved only after 6 and 24 h, respectively.G. C. Wright y D. M. Whitfield: Medición de los potentiates totales y osmóticos en tejidos de alfalfa y girasol usando psicrómetros termopar.