Annals of Botany 72: 37-46, 1993
© 1993 Annals of Botany Company
The Influence of NO-3 and NH+4 Nutrition on the Gas Exchange Characteristics of the Roots of Wheat (Triticum aestivum) and Maize (Zea mays) Plants
Department of Botany, University of Cape Town, Rondebosch, 7700, South Africa
Respiratory oxygen consumption by roots was 1·4- and 1·6-fold larger in NH+4-fed than in NO-3-fed wheat (Triticum aestivum L.) and maize (Zea mays L.) plants respectively. Higher root oxygen consumption in NH+4-fed plants than in NO-3-fed plants was associated with higher total nitrogen contents in NH+4-fed plants. Root oxygen consumption was, however, not correlated with growth rates or shoot:root ratios. Carbon dioxide release was 1·4- and 1·2-fold larger in NO+3-fed than in NH+4-fed wheat and maize plants respectively. Differences in oxygen and carbon dioxide gas exchange rates resulted in the gas exchange quotients of NH-4-fed plants (wheat, 0·5; maize, 0·6) being greatly reduced compared with those of NO-3-fed plants (wheat, 1·0; maize, 1·1). Measured rates of HCO-3 assimilation by PEPc in roots were considerably larger in 4 mM NH+4-fed than in 4 NO-3 plants (wheat, 2·6-fold; maize, 8·3-fold). These differences were, however, insufficient to account for the observed differences in root carbon dioxide flux and it is probable that HCO-3 uptake is also important in determining carbon dioxide fluxes.
Thus reduced root extension in NH+4-fed compared with NO-3-fed wheat plants could not be ascribed to differences in carbon dioxide losses from roots.Copyright 1993, 1999 Academic Press
Triticum aestivum, wheat, Zea mays, maize assimilation, ammonium assimilation, root respiration
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