Root Zone Temperature Effects on Growth and Phosphate Absorption in RapeBrassica napuscv. Emerald

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Abstract
Solution culture experiments with fodder rape (Brassica 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 °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 °C. The minimum phosphate concentration to which plants could lower the culture solution (Cmln) ranged from 0.15 to 2.5 mmol m−3 according to whether roots were at a low (5 °C) or high (35 °C) temperature respectively. The total phosphorus 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.