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Kinetics of ammonium and nitrate uptake by eucalypt roots and associated proton fluxes measured using ion selective microelectrodes

Citation

Garnett, TP and Shabala, SN and Smethurst, PJ and Newman, IA, Kinetics of ammonium and nitrate uptake by eucalypt roots and associated proton fluxes measured using ion selective microelectrodes, Functional Plant Biology, 30, (11) pp. 1165-1176. ISSN 1445-4408 (2003) [Refereed Article]

DOI: doi:10.1071/FP03087

Abstract

Ion-selective microelectrodes were used non-invasively to measure the concentration dependence of NH4 + and NO3 - fluxes around the roots of intact solution-cultured Eucalyptus nitens (Deane & Maiden) Maiden. In addition, NH4 + and H+ fluxes were measured simultaneously at a range of NH 4 + concentrations, and NO3 - and H+ fluxes were measured simultaneously at a range of NO 3 - concentrations. Nitrogen concentrations ranged from 10-250 μM, i.e. in the range corresponding to the high affinity transport system (HATS). Both NH4 + and NO3 - fluxes exhibited saturating Michaelis-Menten-style kinetics. The Km, was 16 μM for NH4 + and 18 μM for NO3 -. Values of Vmax were 53 nmol m-2 s -1 for NH4 + and 37 nmol m-2 s -1 for NO3 -. Proton fluxes were highly correlated with NH4 + and NO3 - fluxes, but the relationships were different. Proton efflux increased with increasing NH4 + concentration and mirrored the changing NH4 + fluxes. The ratio between NH4 + and H+ fluxes was 1:-1.6. Proton influx was evident with initial exposure to NO3 -, with the flux stoichiometry for NO 3 -:H+ being 1:1.4. Subsequent increases in NO3 - concentration caused a gradual increase in H + efflux such that the flux stoichiometry for NO3 -:H+ became 1:-0.8. The presence of 100 μM NH 4 + greatly reduced NO3 - fluxes and caused a large and constant H+ efflux. These results are evidence that E. nitens has a preference for NH4 + as a source of N, and that the fluxes of NH4 + and NO3 - are quantitatively linked to H+ flux.

Item Details

Item Type:Refereed Article
Research Division:Agricultural and Veterinary Sciences
Research Group:Forestry Sciences
Research Field:Tree Nutrition and Physiology
Objective Division:Plant Production and Plant Primary Products
Objective Group:Environmentally Sustainable Plant Production
Objective Field:Environmentally Sustainable Plant Production not elsewhere classified
Author:Garnett, TP (Dr Trevor Paul Garnett)
Author:Shabala, SN (Professor Sergey Shabala)
Author:Smethurst, PJ (Dr Philip Smethurst)
Author:Newman, IA (Dr Ian Newman)
ID Code:28540
Year Published:2003
Web of Science® Times Cited:28
Deposited By:Physics
Deposited On:2003-08-01
Last Modified:2004-04-07
Downloads:0

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