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

Three-month-old Carrizo citrange (hybrid of Citrus sinensis L. Osbeck x Poncirus trifoliata Blanco) seedlings were grown in controlled environment chambers 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 roots, 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-15 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 Botany Company.