VARIATIONS IN WATER AVAILABILITY AND TEMPERATURE IN THE ROOT ENVIRONMENT DURING ROOT VOLUME RESTRICTION STUDIES

Variations were investigated in matric potential (Psi(ms)) and tempera ture in the root environment of tomato plants (Lycopersicon esculentum Mill. 'Red Dwarf) grown over a range (200, 400, or 800 cm(3)) of root ing volumes (RV). Under media-based growing conditions, Psi(ms) and te mperature varied inversely with RV. The root environment in the smalle st RV had a 2-fold decrease in Psi(ms) to -14 kPa, a greater rate of d ecrease in Psi(ms) and a lower overall Psi(ms) magnitude of-30 kPa (co mpared with -12 kPa in the largest RV). There were large diurnal tempe rature fluctuations (range = 12 degrees C) and the root environment in the smallest RV was consistently 3 degrees C higher with a mean of 25 .4 degrees C, compared with a mean of 22.3 degrees C in the largest RV . Enclosing the pots within a modified hydroponic system, in conjuncti on with a very frequent watering regime, eliminated differences in Psi (ms) and reduced differences in media temperature between different RV s. The physiological basis of the dwarfing response previously associa ted with RVR may have been inadvertently confounded with variations in media Psi(ms) and media temperature.