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In the present study, we investigated the effects of increasing salinity on growth, gas exchange, abscisic acid (ABA), calmodulin (CaM), and the relevance to salt tolerance in seedlings of Populus euphratica Oliv. and cuttings of P. "pupularis 35-44" (P. popularis) and P. × euramericana cv. I-214 (P. cv. Italica). The relative growth rates of shoot height (RGR H ) for P. cv. Italica and P. popularis were severely reduced by increasing salt stress, whereas the growth reduction was relatively less in P. euphratica. Similarly, P. euphratica maintained higher net photosynthetic rates (P n ) and unit transpiration rates (TRN) than P. cv. Italica and P. popularis under conditions of higher salinity. Salinity caused a significant increase in leaf ABA and CaM in the three genotypes after the onset of stress, but NaCl-induced ABA and CaM accumulation was more pronounced in P. euphratica, suggesting that P. euphratica plants are more sensitive in sensing soil salinity than the other two poplars. Furthermore, P. euphratica maintained relatively higher ABA and CaM concentrations under conditions of high salinity. The higher capacity to synthesize stress signals, namely ABA and CaM, in P. euphratica and the contribution of this to the salt resistance of P. euphratica are discussed. (2006). Growth, gas exchange, abscisic acid, and calmodulin response to salt stress in three poplars. J Integrat Plant Biol 48(3), 286−293.