Response of St John’s wort (Hypericum empetrifolium) plants to cadmium (Cd) treatment in relation to substrate acidity/alkalinity

The effect of cadmium (Cd) on growth and Cd accumulation in shoots and roots St John’s wort (Hypericum empetrifolium) was studied over three months in a greenhouse. Plants were cultivated in pots containing a uniform mixture of either acid or alkaline substrate consisting of peat and perlite (1:1 v/v). The pots were arranged in a completely randomized block design within two groups (acid substrate and alkaline substrate) with four Cd treatments (0-control, 1, 2, and 5 mg Cd L-1) and six replicates per treatment. Cadmium was applied as CdSO4*8/3H2O. The total amount of Cd applied per pot was 260 ml, corresponding to 0.26, 0.52, and 1.3 mg Cd per pot for doses 1, 2, and 5 mg L-1, respectively. No visual symptoms of toxicity or nutrient deficiency, as well as no differences in plant height were observed in response to Cd application, irrespective of the growth stage or substrate. There were also no differences in height development rate between the plants grown in an acidic or alkaline substrate. Cd accumulation in shoots and roots increased with increasing concentrations of applied Cd and was higher in the acidic substrate. Thus, St John’s wort plant is a Cd accumulator, especially in an acidic environment, and this in combination with its high tolerance to Cd, makes it a suitable species to remove Cd from cadmium-contaminated sites. However, for its use in the preparation of medical products, St John’s wort must be grown in a Cd-free soil so as not to pose a risk to human health. Cd extraction by (DTPA-TEA) can be employed to predict Cd accumulation in this plant.