Cadmium uptake by cucumber plants as affected by fluctuations in nutrient solution cadmium concentration during growth

A nutrient solution experiment was performed to assess the importance of fluctuations in substrate cadmium (Cd) concentrations during plant growth on Cd uptake by cucumber plants (Cucumis sativus L.). Nutrient solution Cd was varied between 0 and 5 mu g L-1 in a way that the average Cd concentration over the entire growth period was 2.5 mu g L-1 for all treatments. Slight but significant (p=0.05) differences in shoot dry matter yield reflected a negative effect of Cd on growth. Alternating Cd in solution every two days between 1.5 and 3.5 mg L-1 or between 0 and 5 mu g L-1 had no different effect than supplying a constant Cd level of 2.5 mu g L-1 during growth and indicated a linear response of the plant to substrate Cd concentration. Experimental treatments where Cd in solution either decreased or increased during the growing period resulted in a lower and a higher plant Cd concentration, respectively, compared to the treatment involving a constant solution Cd concentration of 2.5 mu g L-1, Short time random fluctuations in solution Cd concentration will not influence the final Cd concentrations in crops. Prediction of Cd uptake from soil extraction data will be most reliable when based on a good estimate of the average soil solution concentration towards the end of the plant growing period.