Effect of external potassium (K) supply on the uptake of 137Cs by spring wheat (Triticum aestivum cv. Tonic): a large-scale hydroponic study

A large-scale hydroponic experiment was carried out in a non-controlled greenhouse. Spring wheat plants were grown to maturity at four levels of external K concentration (2, 4, 20 and 40 mg l−1) and one concentration of radiocaesium (8 Bq ml−1). Concentrations of K and radiocaesium in the growth solution were closely monitored, and replenishments were made upon depletion. K effectively competed with radiocaesium in terms of root uptake. Activity concentrations of radiocaesium in plants differed significantly between the four K treatments; the activity concentration at the lowest external K concentration being 100 times higher than that at the highest K level. The relationship between radiocaesium uptake and external K level could be described by a negative power function; this showed that when the K level reached around 12 mg l−1, further increases in the external K level resulted only in slight changes in its inhibitory effect. As a result of this inhibitory effect of potassium supply, concentrations of radiocaesium in plant tissues, grains in particular, were greatly reduced at high external K concentration. Mechanisms involved in Cs–K interaction in root uptake are also discussed.