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Cyclic Variations in Nitrogen Uptake Rate in Soybean Plants: Uptake During Reproductive Growth

J. KEVIN VESSEY, C. DAVID RAPER, JR. and LESLIE TOLLEY HENRY
Journal of Experimental Botany
Vol. 41, No. 233 (December 1990), pp. 1579-1584
Published by: Oxford University Press
Stable URL: http://www.jstor.org/stable/23693376
Page Count: 6
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Cyclic Variations in Nitrogen Uptake Rate in Soybean Plants: Uptake During Reproductive Growth
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Abstract

Net uptake of $\mathrm{N}{\mathrm{O}}_{3}^{-}$ by non-nodulated soybean plants [Glycine max (L.) Merr. cv. Ransom] growing in flowing hydroponic culture was measured daily during a 63 d period of reproductive development between the first florally inductive photoperiod and late seed growth. Removal of $\mathrm{N}{\mathrm{O}}_{3}^{-}$ from a replenished solution containing 1.0 mol m-3 $\mathrm{N}{\mathrm{O}}_{3}^{-}$ was determined by ion chromatography. Uptake of $\mathrm{N}{\mathrm{O}}_{3}^{-}$ continued throughout reproductive development. The net uptake rate of $\mathrm{N}{\mathrm{O}}_{3}^{-}$ cycled between maxima and minima with a periodicity of oscillation of 3 to 7 d during the floral stage and about 6 d during the fruiting stage. Coupled with increasing concentrations of carbon and C:N ratios in tissues, the oscillations in net uptake rates of $\mathrm{N}{\mathrm{O}}_{3}^{-}$ are evidence that the demand for carbohydrate by reproductive organs is contingent on the availability of nitrogen in the shoot pool rather than that the demand for nitrogen follows the flux of carbohydrate into reproductive tissues.

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