RISK ASSESSMENT AND REMEDIATION OF SOIL AND AMENDMENT TRACE ELEMENTS
Title: Effects of Cadmium on Nickel Tolerance and Accumulation in Alyssum species and Cabbage Grown in Nutrient Solution
| Li, Yin-Ming - VIRIDIAN, HOUSTON, TX |
| Chen, Kuang-Yu - UNIV MD, COLLEGE PARK |
| Angle, J Scott - UNIV GA, ATHENS |
| Baker, Alan - MELBOURNE UNIV,AUSTRALIA |
Submitted to: Plant and Soil
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: May 20, 2008
Publication Date: July 18, 2008
Citation: Chaney, R.L., Li, Y., Chen, K., Angle, J., Baker, A.J. 2008. Effects of Cadmium on Nickel Tolerance and Accumulation in Alyssum species and Cabbage Grown in Nutrient Solution. Plant and Soil Journal. 311:131-140.
Interpretive Summary: Our team conducted research to develop methods to use natural nickel hyperaccumulator species such as Alyssum murale to phytoextraction soil Ni for either phytoremediation or phytomining of nickel and cobalt contaminated or mineralized soils. These plants can accumulate up to 2% Ni in dry shoots when growing in natural serpentine soils. Such soils are very unusual in having a high Mg/Ca ratio that inhibits growth of most plants and causes selection of endemic plant species well adapted to the high soil Ni and Mg levels. On the other hand, all plants require Ca for growth, and Ca was known to reduce the phytotoxicity of Ni to crop plants. Previous research in the effect of Ca and Mg on uptake and toxicity of Ni was inconclusive, so we conducted a nutrient solution test of whether higher Ca supply reduced hyperaccumulation or Ni. Two Ni hyperaccumulator Alyssum species (Alyssum murale (from Panorama, Thessaloniki, Greece) and A. pintodasilvae (from Braganca, Portugal) were grown in comparison with the crop plant cabbage (Brassica oleraceae var. capita)) in nutrient solution with high Mg levels and varied Ca levels from very low to high. The results were striking in that Ca did not reduce Ni hyperaccumulation unless very high Ca was supplied, but at the same time, higher Ca reduced the toxicity of Ni to the plants. These finding indicate that Ca fertilization of natural low Ca serpentine soils should improve Alyssum yield and Ni hyperaccumulation. This finding will need to be examined in candidate soils for Ni phytomining to assure that the nutrient solution tests were applicable to soil grown plants.
Nickel phytoextraction using hyperaccumulator plant species to accumulate Ni from mineralized and contaminated soils rich in Ni is an emerging technology. Serpentinite derived soils which contain Ni ore value have a very low ratio of Ca:Mg among soils due the nature of the parent rock. In crop plants, soil Ca reduces Ni phytotoxicity, and the low Ca of serpentine soils could limit hyperaccumulator plant tolerance of serpentine soils used for commercial phytoextraction. In this study, we investigated the effects of varied Ca concentration in the presence of high Mg characteristic of serpentine soils on Ni uptake and tolerance by two serpentine-endemic Alyssum species in comparison with the cabbage (Brassica oleraceae var. capita) in a nutrient solution study. Varied solution concentrations of Ni (31.6-1000 µM for Alyssum, 1.0-10 µM for cabbage) and Ca (0.128-5 mM) were used in a factorial experimental design; 2 mM Mg was used to mimic serpentine soils. Alyssum spp. showed much greater tolerance to high Ni, high Mg, and low Ca solution concentrations than cabbage. For Alyssum spp., Ni induced phytotoxicity was only apparent at 1,000 µM Ni with relatively low and high Ca/Mg quotient. In the 1,000 µM Ni treatment, shoot Ni concentrations ranged from 8.18 to 22.8 g kg-1 for A. murale and 7.60 to 16.0 g kg-1 for A. pintodasilvae. The normal solution Ca concentration (0.8-2 mM) gave the best yield across all Ni treatments for the Alyssum species tested. It was clear that solution Ca levels affected shoot Ni concentration, shoot yield and Ni translocation from root to shoot, but the relation was non-linear, increasing with increasing Ca up to 2 mM Ca, then declining at the highest Ca. Our results indicate that Ca addition to high Mg serpentine soils with very low Ca:Mg ratio may reduce Ni phytotoxicity and improve annual Ni phytoextraction by Alyssum hyperaccumulator species.