Cyclic variations in nitrogen uptake rate of soybean plants:  effects of external nitrate concentration.
Net uptake of NO3- by non-nodulated soybean plants [Glycine max (L.) Merr. cv. Ransom] growing in flowing hydroponic cultures containing 0.5, 1.0 and 10.0 mol m-3 NO3- was measured daily during a 24-d period of vegetative development to determine if amplitude of maximum and minimum rates of net NO3- uptake are responsive to external concentrations of NO3-.  Removal of NO3- from the replenished solutions during each 24-h period was determined by ion chromatography.  Neither dry matter accumulation nor the periodicity of oscillations in net uptake rate was altered by the external NO3- concentrations.  The maxima of the oscillations in net uptake rate, however, increased nearly 3-fold in response to external NO3- concentrations.  The maxima and minima, respectively, changed from 4.0 and 0.6 mmol NO3- per gram root dry weight per day at an external solution level of 0.5 mol m-3 NO3- to 15.2 and -2.7 mmol NO3- per gram root dry weight per day at an external solution level of 10.0 mol m-3 NO3-.  The negative values for minimum net uptake rate from 10.0 mol m-3 NO3- solutions show that net efflux was occurring and indicate that the magnitude of the efflux component of net uptake was responsive to external concentration of NO3-.
Tolley-Henry
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L
Department of Forestry, North Carolina State University, Raleigh 27695-8002, USA.
Raper
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CD
Granato
T C
TC
D050260:Carbohydrate Metabolism; D002244:Carbon / Q000378:metabolism*; D003470:Culture Media; D005308:Fertilizers; D018527:Hydroponics; D009566:Nitrates / Q000493:pharmacokinetics*; D009584:Nitrogen / Q000378:metabolism* / Q000493:pharmacokinetics; D018515:Plant Leaves / Q000378:metabolism; D018517:Plant Roots / Q000378:metabolism; D018520:Plant Shoots / Q000378:metabolism; D013025:Glycine max / Q000378:metabolism*; D013997:Time Factors
D003470:Culture Media; D005308:Fertilizers; D009566:Nitrates; D002244:Carbon; D009584:Nitrogen