Root Zone Temperature Effects on Growth and Nitrate Absorption in Rape (<i>Brassica napus</i>cv. Emerald)

Abstract

Effects of root temperatures, ranging from 10–35 ° C, on growth and nitrate inflow of fodder rape seedlings (cv. Emerald) were examined. These were cultured in solution, with their shoots held at 25 ° C. Nitrate inflow (uptake rate per unit root length) was little affected over the temperature range 10–30 ° C, although enhanced values were found at 35 ° C. Nitrate absorption by roots at 10-30 ° C depleted solution concentrations to an apparent minimum of approximately 6.0 μM NO3−. Relative growth rates were highest with root temperatures of 25 ° C and 30 °C, and these were associated with the greatest nitrate depletion rates from solution. Root: shoot weight ratios were also greatest at 25 °C and 30 °C. At 10 °C and 35 °C a relatively large shoot on a small root maintained nitrate inflow in spite of the plants' slow growth rate. The nitrogen concentration in the shoots was little affected by root temperature. Slow growth at a root temperature of 10 °C was not associated with a shortage of nitrogen in the shoots. The principal influence of temperature appears to be on extension and differentiation of root tissues, possibly through effects on carbohydrate supply to root meristems.