Soil salinity regulates metal bioavailability and soil–plant transfer in halophytic crops

Introduction Soil salinity fundamentally reshapes geochemical controls governing metal mobility and plant uptake, yet its effects across soils with different salinity histories remain poorly resolved. Methods We conducted four controlled experiments using NaCl treatments ranging from 1.0 to 20.0 dS m −1 , combining freshly salinized soils with soils previously exposed to salinity, and evaluated metal behavior in soil -plant systems of Tetragonia tetragonioides and Portulaca oleracea . Results Increasing salinity reduced the solubility and CaCl 2 -extractable (bioavailable) fractions of Fe, Zn, Ba, Sr, and Cu, while total soil metal pools remained largely unaffected, indicating ionic competition, chloride complexation, and ionic-strength -driven shifts in metal partitioning. These patterns show that the observed reductions primarily involve bioavailable metal fractions rather than changes in total soil metal concentrations. Discussion Our findings indicate that especially long-standing soil salinity acts as an important regulator of metal bioavailability and soil -plant transfer, providing mechanistic insight into metal dynamics in saline agroecosystems and supporting the strategic use of halophytes for managing metal-affected saline soils.