Journal of Experimental Botany, Vol 49, 721-730, Copyright © 1998 by Oxford University Press
R Cardenas-Navarro, S Adamowicz and P Robin
A simple model is proposed to describe diurnal net nitrate uptake rate
patterns observed experimentally on young plants grown under constant
non-limiting nutrition. It rests on two hypotheses: net uptake rate is
under negative feedback control by internal plant nitrate content, and
nitrogen metabolism occurs only during the light period. The model
parameters were determined from the results of three independent
experiments performed under non-disturbing conditions in a growth room at
constant air and solution temperatures. Net hourly nitrate uptake rate was
measured through a diurnal cycle and after an extended 28 h period of
darkness. It increased continuously during the light period and decreased
during the dark period. Under prolonged darkness, net uptake declined to an
asymptotic positive uptake rate of about 10-5 mol
h-1 g-1 total plant dry
weight. The measured hourly nitrate uptake rate values were consistent with
independent determinations of long-term nitrate and total N accumulations
in the plant. Realistic simulations of experimental data are achieved with
the proposed model. Furthermore, the maintenance of a positive net uptake
rate, measured in non-growing plants subjected to prolonged darkness, is
explained in the model by the continuous increase of plant water content.
The importance of the diurnal variations of plant water content for nitrate
uptake rate is emphasized and gives consistency to the homeostasis
hypothesis of the model. The diurnal changes in nitrate uptake predicted by
the model are strongly dependent on the assumption made for diurnal changes
in nitrate assimilation. While the purely photosynthetic assumption is
convenient, a more realistic metabolism sub-model is
needed.Keywords: Light/dark cycles, day, night, water
content, nitrogen, hydroponic.
ARTICLES
Diurnal nitrate uptake in young tomato (Lycopersicon esculentum Mill.) plants: test of a feedback-based model
Ecophysiologie et Horticulture, INRA, Domaine St Paul, Site AGROPARC, F-84914 Avignon Cedex 9, France; Corresponding author; e-mail: adamow@avignon.inra.fr
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