The restoration of saline grasslands relies on effective soil amelioration， precise seeding timing， and successful seedling establishment. In this study， the pioneer grass species Leymus secalinus was used as test material， and low， medium， and high salinity levels of salt stress were set up using a 1∶2 ratio of NaCl and Na₂SO₄. The effects of salt stress and its interaction with seedling age on root system phenotypic plasticity were investigated. Our results showed that salt stress made roots grow shallower. Seedling age was the main factor controlling root biomass distribution （P<0.001）. Salt alone and its interaction with age were only significant in some cases. Salt and age both reduced root length， surface area， and volume （P<0.01）. Their interaction had the strongest effect on root volume （F=36.878）. Salt damage increased nonlinearly as the seedling grew. Root tip number decreased with higher salt. Older seedlings were more sensitive to salt. Root angle significantly reduced at the two- and three-leaf stages. Also， root fractal dimension showed a nonlinear response， and increased under low salt but decreased under medium and high salt （P<0.05）. This study revealed the phased adaptation strategies of Leymus secalinus seedlings under salt stress， providing a basis for enhancing the application potential of Leymus secalinus in ecological restoration of saline grasslands.

Leymus secalinus  /  Salt stress  /  Seedling age  /  Root system  /  Phenotypic plasticity