Effect of salinity on the growth performance and macronutrient status of four citrus cultivars grafted on trifoliate orange

To test the scions whether or not affect salt tolerance of citrus at the whole-plant level, four common cultivars belonging to sweet oranges (Newhall and Lane late) and loose-skin mandarins (Egan#1 and Guoqing#1) were grafted on trifoliate orange, and exposed to 0, 30, 60 or 90 mM Sodium chloride (NaCl). Results showed that, the NaCl treatment induced less reduction in dry weight (DW), leaf area, photosynthetic rate (PN) but greater reduction in leaf transpiration rate (Tr) in loose-skin mandarins than in sweet oranges. It was further found that the loose-skin mandarins accumulated less Na+ and Cl- in leaves while more of these ions in their roots. Additionally, the changes in main nutrient contents varied among the salt-treated cultivars, and the loose-skin mandarins showed less decreases of leaf Mg2+ and Ca2+. Overall, our results revealed that the different cultivars grafted on the same rootstock showed differences in growth performance and ions distribution under salinity. Higher salt tolerance shown by loose-skin mandarins may depend on the ability of excluding Na+ and Cl- from leaves and also be associated with maintaining nutritional homeostasis especially the balance of Mg+and Ca2+ in their leaves.   Key words: Citrus, leaf gas exchange, nutrient concentrations, plant growth, salt tolerance.