Influence of Chloride and Transpiration on Net15NO3−Uptake Rate byCitrus Roots

Three-month-old Carrizo citrange (hybrid of Citrus sinensis L. Osbeck× 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 m m15 NO 3 K (96% atom excess 15 N) solution, and transpiration as well as concentration of 15 N and Cl − in roots, stem and leaves were measured after 24 h. Transpiration and 15 NO 3− 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 NO 3− absorption, net 15 NO 3− 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 NO 3− uptake was more closely related to Cl − antagonism from salt stress than to reduced transpiration rate.