Advances in the use of Halimione portulacoides stem cuttings for phytoremediation of Zn-polluted soils

The salt-marsh shrub Halimione portulacoides can grow in soils containing extremely high concentrations of Zn and stem cuttings have recently been shown to aid the recovery of polluted soils although further work on this methodology have is required. A greenhouse experiment was carried out to analyze the effects of a range of Zn concentrations (0–130 mmol l−1) on the establishment, growth and photosynthetic performance of stem cuttings of different sizes of Halimione portulacoides, with the aim of determine the phytotoxicity thresholds and the optimal initial size of the cuttings to be used in phytoremediation strategies. Stem cuttings were able to survive and grow at external Zn concentrations of 130 mmol l−1. Plants from smaller cuttings showed greater growth inhibition, which could have been related to the inability to establish a root system sufficiently developed so as to avoid the translocation of Zn to aerial parts. The present study demonstrates that stem cuttings of H. portulacoides can establish and develop a root system under concentrations as high as 130 mmol l−1 Zn (approximately 9000 mg kg−1). In highly polluted soils, with concentrations from 50 mmol l−1, it would be advisable to use stem cuttings with a minimum size of approximately 10 cm in length and a minimum biomass of 100 mg dry weight. This study indicate that the use of H. portulacoides stem cuttings could play an important role in the restoration of coastal ecosystems contaminated with heavy metals.