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Mature plants of Calluna vulgaris. Trifolium repens and Agrostis capillaris were dug up from field sites. Plants were artificially labelled with 137Cs by uptake through the roots from a liquid medium. Shoot material was allowed to dry to give plant litters adequately labelled for leaching experiments, using microcosms subjected to a number of applied treatments. Measurements were made of 137Cs activity, potassium content and pH on the leaches from each micrososm obtained every 2 weeks over a 3-month period. The respiration rate of the litter was also measured to give an index of microbial activity. At the end of the experiment. 137Cs and K contents of the residual litter were measured. Generally, the rate of release of 137Cs from Calluna litter was slower than that from Trifolium or Agrostis. After 3 months, the loss of 137Cs from Calluna litter had stabilised at about 30–40% of the original (i.e. 60–70% remained in the litter). Trifolium had lost 60% of the initial 137Cs over the same period, whilst Agrostis had lost about 70%. Repeated drying and rewetting treatment, compared to a continuous moistened state, resulted in the stabilisation of 137Cs within Trifolium and Agrostis litters. In Agrostis and Trifolium, the release of potassium was greater and more rapid than the release of 137Cs, with only 10% of the original K remaining in the litter after 2 months. In Calluna, the release of K resembled the release of 137Cs more closely.

Agrostis capillaris (Agrostis) and Calluna vulgaris (Calluna), two species with differing phenologies and widespread presence in upland areas of Britain where high Chernobyl fallout occurred, were grown in pot culture with varying concentrations of potassium in the rooting medium. Tissue content of potassium increased with increasing supply in both species. Roots, excised from these plants, were placed in a solution of 137-Cs-labelled caesium chloride for 15 min to determine uptake potential. There were clear negative relationships between the rate of uptake of 137Cs by both species and (a) the concentration of potassium supplied and (b) plant tissue potassium concentrations. With Agrostis, there was an approximately ten-fold difference in 137Cs uptake between potassium-deficient and optimum plants; with Calluna, it was approximately eight-fold. These results demonstrate the suppression of 137Cs uptake into plants by potassium supply.