Cd extraction potential of Thlaspi caerulescens in extracontinental climate conditions (Zakamensk, Buryatia, Russia)

摘要

Thlaspi caerulescens is known to be a Cd hyperaccumulator used in a number of countries for remediation of the contaminated areas. The objective of the study was to investigate Cd uptake by this plant in extracontinental climatic conditions of Buryatia. Performed experiments included a study of the following factors affecting Cd accumulation by the plant: 1) levels ofCd contamination of the soil; 2) soil Cd availability to plants; 3) time period of the plant — contaminated soil interaction. Cd contamination was simulated by addition of different Cd doses (0; 1;5; 10; 50; 100; 200; 500 mg/kg) to native soil sample. To facilitate phytoextraction 3 mmol/kgofEDTA was used as background for similar Cd doses. After Cd and EDTA application the soil was incubated for 30 and 365 days before planting. Obtained data showed that toxical, neutral or stimulating Cd effect in T. caerulescens depended upon the applied Cd doses and the soil incubation period. Cd doses from 1 to 200 mg/kg resulted in a corresponding decrease of plant biomass and those ranging from 200 to 500 mg/kg terminated germination of plant seeds sown in contaminated soil after its 30 day incubation. However the increased period of incubation (365 days) prior to seeding diminished metal toxicity for plants and soil Cd doses of 1 to 10 mg/kg stimulated the biomass growth by 13% versus control. At maximum Cd dose of 500 mg/kg shoots accumulated 259 mg/kg of Cd in dry mass and the root system up to 609 mg/kg. Removal of soil Cd by plants per square unit varied from 0.13 to 12.92 mg/m~2 depending upon Cd dose in soil and its incubation period. In experiment with 30 day soil incubation maximum Cd removal was observed for Cd dose of 50 mg/kg, while after 365 day incubation maximum removal effect was registered for a higher Cd dose of 100 mg/kg. Application of EDTA in the dose of 3 mmol/kg as a background substance to mobilize soil Cd proved to be toxic and therefore unreasonable since no germination took place. The experiments showed that Cd extraction potential of T. caerulescens in arid soils of Buryatia is low as compared to published data and complete remediation of the soils containing from 1 mg/kg to 10 mg/kg of Cd requires no less than two to ten harvests.