Salinity influences Cd accumulation and distribution characteristics in two contrasting halophytes, Suaeda glauca and Limonium aureum.

Abstract

The potential for the phytoremediation of halophytes has been widely recognized. However, the effects of salt on Cd accumulation characteristics in different halophytic species, which may also be related to their salt tolerance, are still unclear. This study investigated the effects of salinity on Cd accumulation and distribution in two distinct halophytes, Suaeda glauca (euhalophyte) and Limonium aureum (recretohalophyte). Seedlings of the two species were treated with 0, 3, and 6mgkg-1 soil Cd in combination with or without 0.3% NaCl in a pot experiment. The amount of Cd within the rhizosphere and plant tissues, plant biomass, and the subcellular distribution and chemical forms of Cd were examined. Results showed that the addition of NaCl significantly increased Cd bioavailability at high Cd levels due to the rhizosphere acidification effect. Meanwhile, salinity differently impacted plant biomass allocation, and enhanced Cd uptake and translocation in both studied halophytes. Excess Cd was excreted from the leaf surface, possibly by salt glands of L. aureum, with the salinity facilitating this process. Majority of the Cd was found within the cell walls and vacuolar compartments of two species. However, S. glauca plants had higher proportions of inactive Cd (extracted by 2% HAc and 0.6M HCl) and lower proportions of active Cd (extracted by 80% ethanol and water), as opposed to L. aureum, which would better inform S. glauca's higher Cd accumulation. Based on these results, S. glauca seems more applicable for phytomanagement of Cd-contaminated saline soils due to its higher capacity for Cd enrichment and tolerance amplified by NaCl.