Effects of zinc and lead on seed germination of Helichrysum microphyllum subsp. tyrrhenicum, a metal-tolerant plant

The seed germination of Helichrysum microphyllum subsp. tyrrhenicum, an endemic species of Sardinia and Corsica with metal tolerance capability, was evaluated against zinc (Zn; 0, 250, 500 and 1000 mg/L) and lead (Pb; 0, 25, 50 and 100 mg/L) stress. Seeds were collected in three localities: (a) inside a mine dump highly polluted with these metals, (b) outside but close to this area and (c) far from the metal-polluted site. Germination responses were assessed at 10, 15 and 20 degrees C, and the percentage, time of germination and mortality of seedlings were evaluated. The taxon showed a high capacity to germinate under Zn and Pb stress, and the germination was never completely inhibited; however, the germination decreased with increasing Zn concentrations, but not under Pb stress. Moreover, the seeds from specimens growing in mining sites appeared to be less affected by Zn stress than seeds coming from the other localities. A successful survival of seedlings during the first days of their development under metal stress and under controlled conditions was detected. Our study suggests that this species may give an important contribution to future phytoremediation programs on mining sites, in which it could be spread by seeds in order to form a vegetation cover.