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Elevated [CO2] and salinity in the soils are considered partof the effects of future environmental conditions in arid and semi-arid areas. While it is known that soil salinization decreases plant growth, an increased atmospheric [CO2] may ameliorate the negative effects of salt stress. However, there is a lack of information about the form in which inorganic nitrogen source may influence plant performance under both conditions. Single factor responses and the interactive effects of two [CO2] (380 and 800 ppm), three different NO3-/NH4+ ratios in the nutrient solution (100/0, 50/50 and 0/100, with a total N concentration of 3.5 mM) and two NaCl concentrations (0 and 80 mM) on growth, leaf gas exchange parameters in relation to root hydraulic conductance and N-assimilating enzymes of broccoli (Brassica oleracea L var. Italica) plants were determined. The results showed that a reduced NO3- or co-provision of NO3- and NH4+ could be an optimal source of inorganic N for broccoli plants. In addition, elevated [CO2] ameliorated the effect of salt exposure on the plant growth through an enhanced rate of photosynthesis, even at low N-concentration. However, NO3- or NO3-/NH4+ co-provision.display differential plant response to salt stress regarding water balance, which was associated to N metabolism. The results may contribute to our understanding of N-fertilization modes under increasing atmospheric [CO2] to cope with salt stress, where variations in N nutrition significantly influenced plant response. (C) 2016 Elsevier B.V. All rights reserved.