Submitted to: Plant and Soil
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/13/2005
Publication Date: 3/15/2006
Citation: Wang, A., Angle, J.S., Chaney, R.L., Mcintosh, M.S. 2006. Soil ph effects on uptake of cd and zn by thlaspi caerulescens. Plant and Soil. 281(1-2):325-337. Interpretive Summary: Some soils require cadmium removal to protect food safety or comply with government limitations. Phytoextraction of soil cd is under development because it can remove soil Cd at lower cost than other proposed methods, especially using southern France genotypes which accumulate 10-times high Cd concentration than previously studied strains. Because lowering soil pH increases accumulation of Cd and Zn by Thlaspi caerulescens, it is likely that field pH would be lowered to decrease the cost of remediation, but lowering pH could allow the high soil Cd and Zn to harm soil microbes needed to maintain soil fertility and function (or ecology). In this experiment two soils collected at different fields near a Zn smelter at Palmerton, PA, were adjusted to 5 or 6 pH levels from initial pH about 7 to a lowest pH of about 4.7. Thlaspi caerulescens was grown for 6 months and analyzed. Results both confirm the ability of the southern France genotypes to accumulate remarkable levels of Cd. As pH was lowered, concentration of Cd in the plant shoots rose until about pH 6, and then declined, while shoot biomass yield declined more sharply at lower pH, so that shoot total Cd was substantially reduced at the lower pH levels studied. Other papers will report the effects of the pH lowering on soil microbial activities, and whether growing Thlaspi protected soil microbes from adverse effects of the more acidic Zn+Cd contaminated soils. In this test using southern France Thlaspi, up to 45 and 37% of total soil Cd was removed from by the 6 month growth of Thlaspi, confirming the high promise of managed phytoextraction to remediate Cd risk from soils.
Technical Abstract: For phytoextraction to be successful and viable in environmental remediation, strategies that can optimize plant uptake must be identified. Thlaspi caerulescens is an important hyperaccumulator of Cd and Zn, whether adjusting soil pH is an efficient way to enhance metal uptake by T. caerulescens must by clarified. This study used two soils differing in levels of Cd and Zn and which were adjusted to 5 or 6 different pH levels. 0.1 M Sr(NO3)2 extractable metals in soil, and T. caerulescens tissue metal concentrations were measured. The soluble metal form of both Cd and Zn was greatly increased with decreasing pH. Reducing pH significantly influenced plant metal uptake. For the high metal soil, highest plant biomass was at the lowest soil pH (4.74). The highest shoot metal concentration was at the second lowest pH (5.27). For low metal soil, due to low pH induced Al and Mn toxicity, both plant growth and metal uptake was greatest at intermediate pH levels. The extraordinary Cd phytoextraction ability of T. caerulescens was further demonstrated in this experiment. In the optimum pH treatments, Thlaspi caerulescens extracted 45% and 37% of total Cd in the low and high metal soils, respectively, with just one planting. Overall, reducing pH is an effective strategy to enhance phytoextration. However, a different optimum pH may exist for individual soils. This pH should be identified to avoid unnecessarily extreme acidification of soils.