Effects of phytoextraction on added Ni and chief chemical properties in soils

In recent years,phytoremediation using metal hyperaccumulators has been proposed as a cost-effective and environmen- tally-friendly solution to the problem of heavy metal contaminated soils.Researchers have been playing attention on the mechanism of hyperacumulator uptake heavy metals and the biological and chemical effects of heavy metal pollution in soil-plant system.For those purposes,greenhouse pot experiment was employed in this study.Alyssum murale,a species of Ni hyperaccumulators,were planted in soils with 7 different Ni concentrations ranging from 0 to 1 600 mg kg-1 added in the form of NiSO 4to investigate the ef- fects of phytoextraction on Ni fraction redistribution,soil pH and organic carbons.After 110 days of planting,several plant and soil indices,including soil nickel concentration,plant nickel concentration,soil pH values,soil organic carbon,were studied.The results showed that DTPA-Ni in the rhizospheric soils decreased considerably,compare with that in the non-rhizospheric soils.The ratio of DTPA-Ni in the rhizospheric soils to that in the non-rhizospheric soils ranged from 0.33 to 0.61.The amounts of Ni extracted by plants ranged from 6.61mg to 31.18 mg per pot,which had increased with increasing Ni concentrations in soils.The highest concen- tration of Ni in the shoots was 12 454.1 mg kg-1 at 1 600 mg Ni kg-1 treated soil.The redistribution index in the different Ni treated rhizospheric soils ranged from 2.17 to 4.19,which were lower considerably than that in the non-rhizospheric soils,ranged from 6.87 to 15.91.The binding intensity index was lower with increasing the amounts of added Ni,which ranged from 0.84 to 0.39 in rhizospheric soils and from 0.88 to 0.26 in non-rhizospheric soils,respectively.Therefore,phytoextraction can accelerate the stabili- zation of added soluble Ni in soils.Our results also found that,compare with control soils,phytoremediation may raise the soil pH values and the contents of organic carbon in soils.In conclusion,phytoextraction can extract the heavy metal from the contaminated soil and then accelerate metal stabilization in soils.