Plant coexistence can enhance phytoextraction of cadmium by tobacco (Nicotiana tabacum L.) in contaminated soil

A mesocosm experiment was conducted to investigate whether plant coexistence affects cadmium (Cd) uptake by plant in contaminated soil. Tobacco (Nicotiana tabacum L. var. K326) and Japanese clover (Kummerowia striata (Thunb.) Schindl.) were used. Cadmium was applied as 3CdSO4·8H2O in solution at three levels (0, 1, and 3 mg/kg soil) to simulate an unpolluted soil and soils that were slightly and moderately polluted with Cd. Tobacco (crop), Japanese clover (non-crop), and their combination were grown under each Cd treatment. Compared to monoculture and under all Cd treatments, co-planting with Japanese clover did not affect tobacco biomass but significantly increased Cd concentration in all tobacco tissues and enhanced Cd accumulation in tobacco shoots and roots. Compared to monoculture, co-planting reduced soil pH and increased Cd bioavailability. For tobacco, co-planting with Japanese clover increased the Cd bioconcentration factor (BCF) in Cd contaminated soil. Japanese clover also accumulated substantial quantities of Cd in shoots and roots. Thus, total Cd uptake by the plants was much greater with co-planting than with monoculture. The results suggested that phytoextraction can be effectively increased through tobacco co-planting with Japanese clover in mildly Cd-contaminated soil.