title: Cyclic variations in nitrogen uptake rate of soybean plants:  effects of external nitrate concentration.
abstract: 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-.
authors.affiliation: Department of Forestry, North Carolina State University, Raleigh 27695-8002, USA.
authors.forename: L
authors.initials: L
authors.lastname: Tolley-Henry
authors.forename: C D
authors.initials: CD
authors.lastname: Raper
authors.forename: T C
authors.initials: TC
authors.lastname: Granato
mesh_terms: 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
chemical_list: D003470:Culture Media; D005308:Fertilizers; D009566:Nitrates; D002244:Carbon; D009584:Nitrogen