Uptake of cadmium by the invasive perennial weeds Ranunculus repens and Geranium robertianum under laboratory conditions

The objective of this study was to compare the accumulation and partitioning of cadmium (Cd) in a fibrous versus a tap root weed, Ranunculus repens and Geranium robertianum respectively. To meet this objective, we compared the accumulation by and the partitioning of Cd in R repens versus G. robertianum grown in soils spiked with 0.015 grams of Cd for a period of three weeks. The rate of Cd uptake was also compared by following the fate of 109Cd within the root, stem and leaf of the two weeds. Prior to Cd exposure, leaf and stem of control R. repens contained significantly greater amounts of Cd as compared to G. robertianum, whereas Cd concentrations in roots of the control plants for the two species were not significantly different (p > 0.05, student's t-test). Post Cd exposure the two species contained similar amounts of Cd in leaf and stem, however, roots of R. repens contained almost two-fold the amounts of Cd as compared to G. robertianum. Comparison of k (h(-1), rate of 109Cd uptake) for stem, leaf and root of the two species indicated that G. robertianum accumulated 109Cd over the first 24-48 h at a faster rate as compared to R. repens. For both species and all three organs, maximum accumulation of 109Cd occurred within the first 24-48 h. Our findings indicate that the fate of Cd within these two species is quite different with the fibrous root of R. repens serving to accumulate and store Cd whereas in G. robertianum, Cd is rapidly taken up and tends to be accumulated within its leaf.