Cadmium availability to three plant species varying in cadmium accumulation pattern

Plant response to soil Cd is highly variable. Plants varying in Cd accumula tion pattern were evaluated to determine if Cd was taken up from similar or different pools in soils. Three metal-contaminated soils (pH 8) and a nonc ontaminated soil were labeled with Cd-109 using a carrier-free (CdCl2)-Cd-1 09 solution Rye grass (Lolium perenne L.), lettuce (Lactuca sativa L.), and the Zn- and Cd-hyperaccumulator Thlaspi caerulescens J. Presl & C. Presl w ere grown on these soils and harvested. The isotopic composition of Cd in p lant shoots (IC,) was measured and the isotopic composition in the soil sol ution (ICs) was calculated using the isotopic exchange kinetics (IEK) metho d. The Cd concentrations in shoots ranged from 0.1 to 2.3 mg kg(-1) in rye grass, 0.4 to 8.3 mg kg(-1) in lettuce, and 8.7 to 647 mg kg(-1) in T. caer ulescens. The ICp values were similar among species, suggesting that the sa me pool of soil isotopically exchangeable Cd was accessed despite variation s in Cd uptake pattern. The ICP values were similar to the ICs, suggesting that the IEK method assesses the pool that is phytoavailable. Despite the h igh soil pH, more than 50% of the total soil Cd was isotopically exchangeab le within 90 d. Lettuce and rye grass took up less than 1% of the exchangea ble Cd while T. caerulescens extracted up to 22% of this pool. In conclusio n, plants representing a wide array of behavior toward Cd take up the metal from a similar pool of soil Cd, which is assessed by the IEK method.