The role of the quality of soil organic matter in cadmium accumulation in plants

Two acid soils (pHCaCl2 4—4.5) synthesized by mixing 1 part by weight of Carex or Sphagnum peat with 9 parts by weight of clay, were compared in a pot and an incubation experiment. In the pot experiment the experimental plant was the radish, the cadmium content of whose tops rose in the first harvest by 23 mg/kg and in the second by 16 mg/kg when 5.12 mg of cadmium labelled with 115mCd had been added to the mixture of Carex peat and clay (3 kg/pot). The corresponding contents in radishes grown in a mixture of Sphagnum peat and clay were 51 and 33 mg/kg. In the roots, the corresponding contents were only 1/3—1/4 of the preceding. Of the cadmium added to the mixture of Carex peat and clay, radish tops and roots took up an overall 3.9 %. In the mixture of Sphagnum peat and clay the corresponding proportion was 9.5 %. In the incubation experiment, differences in the solubility of the added cadmium accounted satisfactorily for the differences found in the plant experiment. It was concluded from the results of the pot and incubation experiments and from autoradiographic tracings of cadmium uptake in radishes, that radishes were able to take up cadmium dissolved in soil water with little hindrance, and that translocation occurred in the plant in conjunction with the transpiration stream