ROOT ZONE TEMPERATURE EFFECTS ON GROWTH AND PHOSPHATE ABSORPTION IN RAPE BRASSICA-NAPUS CV EMERALD

Solution culture experiments with fodder rape (B. napus cv. Emerald) show that reduced root temperatures appear to have little effect on phosphate inflow over a wide range of P concentration. At a cool root temperature (10.degree. C) plant growth rate was reduced but this was compensated for by a low root:shoot ratio, so that inflow remained relatively steady. An increased inflow per unit length of root was only achieved at an elevated root temperature of 35.degree. C. The minimum phosphate concentration to which plants could lower the culture solution (Cmin) ranged from 0.15-2.5 mmol m-3 according to whether roots were at a low (5.degree. C) or high (35.degree. C) temperature, respectively. The total P concentration in tissues was affected by root zone temperature and at low root temperatures this could be a growth limiting factor. The organic (assimilated) fraction of P in shoot tissues was smaller in low temperature plants. These showed visual symptoms of apparent P deficiency. Levels of inorganic P in roots may also be a factor in feedback of control of inflow.