Influence of chloride and transpiration on net (NO3-)-N-15 uptake rate by Citrus roots

Three-month-old Carrizo citrange (hybrid of Citrus sinensis L. Osbeck x Pon cirus trifoliata Blanco) seedlings were grown in controlled environment cha mbers in pots of fine sand. Plants were irrigated with either non-saline or saline solutions over a 3-week period. After these treatments, plants were transferred to vessels containing a 5 mM (NO3K)-N-15 (96% atom excess N-15 ) solution, and transpiration as well as concentration of N-15 and Cl- in r oots, stem and leaves were measured after 24 h. Transpiration and (NO3-)-N- 15 uptake rates were inhibited after exposure to NaCl and the concentration of salt pre-treatment determined the intensity of this inhibitory effect. To determine the effect of transpiration on NO3- absorption, net (NO3-)-N-1 5 uptake rate was measured in salt stressed and non-stressed plants exposed to different light intensities or relative humidities and also in detached roots. Reduction in NO3- uptake was more closely related to Cl- antagonism from salt stress than to reduced transpiration rate. (C) 1999 Annals of Bo tany Company.