It is unknown whether phenotypic plasticity in fitness-related traits is associated with salinity-sodicity tolerance. This study compared growth and allocation phenotypic plasticity in two species with low salinity-sodicity tolerance (Chenopodium acuminatum and C.stenophyllum) and two species with high salinity-sodicity tolerance (Suaeda glauca and S.salsa) in a pot experiment in the Songnen grassland, China. While the species with low tolerance had higher growth and allocation plasticity than the highly tolerant species, the highly tolerant species only adjusted their growth traits and maintained higher fitness (e.g., plant height and total biomass) in response to increased soil salinity-sodicity, with low biomass allocation plasticity. Most plasticity is apparent plasticity (ontogenetic change), and only a few traits, for example, plant height:stem diameter ratio and root:shoot biomass ratio, represent real plasticity (real change in response to the environment). Our results show that phenotypic plasticity was negatively correlated with saline-sodic tolerance and could be used as an index of species sensitivity to soil salinity-sodicity.