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The Effect of Root Temperature on Growth and Uptake of Ammonium and Nitrate by Brassica napus L. cv. Bien venu in Flowing Solution Culture: II. UPTAKE FROM SOLUTIONS CONTAINING NH 4 NO 3

J. H. MACDUFF, M. J. HOPPER and A. WILD
Journal of Experimental Botany
Vol. 38, No. 186 (January 1987), pp. 53-66
Published by: Oxford University Press
Stable URL: http://www.jstor.org/stable/23691645
Page Count: 14
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The Effect of Root Temperature on Growth and Uptake of Ammonium and Nitrate by Brassica napus L. cv. Bien venu in Flowing Solution Culture: II. UPTAKE FROM SOLUTIONS CONTAINING NH
          4
          NO
          3
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Abstract

The effects of root temperature on uptake and assimilation of $\mathrm{N}{\mathrm{H}}_{4}^{+}$ and $\mathrm{N}{\mathrm{O}}_{3}^{-}$ by oilseed rape (Brassica napus L. cv. Bien venu) were examined. Plants were grown for 49 d in flowing nutrient solution at pH 6.0 with root temperature decrementally reduced from 20 °C to 5 °C; and then exposed to different root temperatures (3, 5, 7, 9, 11, 13, 17 or 25 °C) held constant for 14 d. The air temperature was 20/15 °C day/night and nitrogen was supplied automatically to maintain 10 mmol m—3 NH4NO3 in solution. Total uptake of nitrogen over 14 d increased threefold between 3—13 °C but was constant above 13 °C. Net uptake of $\mathrm{N}{\mathrm{H}}_{4}^{+}$ exceeded that of $\mathrm{N}{\mathrm{O}}_{3}^{-}$ at all temperatures except 17 °C, and represented 47—65% of the total uptake of nitrogen. Unit absorption rates of $\mathrm{N}{\mathrm{H}}_{4}^{+}$ and $\mathrm{N}{\mathrm{O}}_{3}^{-}$ had a 5-fold range and changed with temperature and time; the Q10 values of 0.9—2.0 for $\mathrm{N}{\mathrm{H}}_{4}^{+}$ and of 1.5—2.7 for $\mathrm{N}{\mathrm{O}}_{3}^{-}$ suggested that $\mathrm{N}{\mathrm{O}}_{3}^{-}$ absorption was more sensitive than $\mathrm{N}{\mathrm{H}}_{4}^{+}$ absorption to temperature. Rates of absorption were relatively stable at 3 °C and 5 °C compared with those at 17 °C and 25 °C which increased sharply after 10 d. Tissue concentration of N in the shoot, expressed on a fresh weight basis, was independent of root temperature throughout, but doubled between 3—25 °C when expressed on a dry weight basis. The apparent proportion of net uptake of $\mathrm{N}{\mathrm{O}}_{3}^{-}$ that was assimilated was inversely related to root temperature. The results are used to examine the relation between unit absorption rate and shoot : root ratio in the context of short and long term responses to change of root temperature.

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