Zinc and cadmium uptake from a metalliferous soil by a mixed culture of Athyrium yokoscense and Arabis flagellosa
Populations of Athyrium yokoscense, a fern that hyperaccumulates Zn and Cd, have often been found at abandoned mining sites in Japan, and are often accompanied by another Zn and Cd hyperaccumulating plant, Arabis flagellosa. We compared the Zn and Cd uptake characteristics of At. yokoscense and Ar. flagellosa and examined the influences of community development on Zn and Cd uptake by each plant. A soil culture experiment was conducted using a rhizobox system with seven compartments, each filled with a metalliferous soil taken from Ikuno-cho, Hyogo Prefecture, Japan. The treatments consisted of the following three planting schemes: two plants of At. yokoscense (AY), two plants of Ar. flagellosa (AF) and a mixed planting of two plants of each species (AY+AF). After 3 months of cultivation, the Zn and Cd concentrations in the shoots were approximately 4.0 and 0.9 g kg−1 for At. yokoscense in the AY treatment and 24 and 0.3 g kg−1 for Ar. flagellosa in the AF treatment, respectively. These results indicated that Ar. flagellosa was more efficient at accumulating Zn in the shoots than At. yokoscense. In the AY+AF treatment, the amounts of water-soluble Zn and Cd in the soil of the central compartments were significantly higher than those in the AY and AF treatments. Despite this, the Zn and Cd concentrations in the shoots of Ar. flagellosa in the AY+AF treatment were not significantly different from those in the AF treatment. The Cd content in the shoots of At. yokoscense was higher in the AY+AF treatment than in the AY treatment, owing to a growth enhancement in the AY+AF treatment. Consistent with the results for the AY and AF treatments, Ar. flagellosa accumulated higher shoot concentrations of Zn than At. yokoscense and At. yokoscense accumulated higher concentrations of Cd than Ar. flagellosa in the AY+AF treatment. These results suggested that the levels of Zn and Cd accumulated by these two plants were not largely affected by their community development, and implied that communities of these plants do not develop as a result of mutual effects on metal uptake.