Mercury tolerance study in holm oak populations from the Almadén mining district (Spain)

The Almadén area (Central Spain) has been the mining district with the largest mercury exploitation of the world since Roman times. In this place, the natural vegetation could have undergone heritable adaptations to mercury caused by the long exposure times to this toxic element. The aim of this work is to study if the main arboreal species of the district (Quercus ilex) has been able to develop a heritable tolerance to mercury. For this purpose, six holm oak populations (three from the Almadén mining district and three from an uncontaminated area) were selected. From these populations, hundreds of acorns were collected and then were sown and grown subjected to three mercury solutions (5, 25 and 50 μM Hg). The response to the treatments was evaluated in relation to germination rates, biomass, Hg accumulation and nutrient uptake. On the whole all populations behaved in the same way when subjected to the different treatments. Just one population showed a worse development, probably as a consequence of the negative quality site where the acorns were collected. None of the mercury treatments injured seriously to none of the seedlings, thus Q. ilex seems to be a species more tolerant to mercury than other woody species that have been studied previously (Moreno-Jiménez et al., 2007, 2009).