Phytoremediation in the Guadiamar Green Corridor (SW Spain): Trace element uptake by plants and effects on soil fungal diversity

The responses of plants and their associated microorganisms to trace elements (TE) in soils present different patterns depending on the plant species and the TE concentration. In this work, the behaviours of several plant species growing in the Guadiamar Green Corridor (GGC) (Seville, Spain), contaminated by the Aznalcóllar mine spill, are discussed. Soil fungal diversity and mycorrhizal symbioses with herbaceous and tree species in the area are also summarized. TE accumulation in wild herbaceous plants (Poaceae, Asteraceae, Brassicaceae, and Fabaceae) differed among families and species but, with some exceptions, most of them tended to exclude TE from their aerial biomass. Most of the studied afforested shrubs and tree species in the GGC revealed an exclusion strategy for most of the TE, meaning that these species could be adequate for TE phytostabilization. White poplar accumulated high concentrations of Cd and Zn in its aerial tissues, thus being a good candidate for phytoextraction and biomonitoring of these elements. In contrast, other two native Mediterranean trees, holm oak and wild olive, as well as eucalyptus trees, presented a behaviour of TE exclusion (except for Mn). The study of several native thistles revealed their suitability for bioenergy production, although Cd contents in these plants were usually high compared to reference levels. Regarding fungal mycorrhization, arbuscule abundance in herbaceous roots colonized by arbuscular mycorrhizal fungi (AMF) was reduced by soil contamination. In the case of ectomycorrhizal (ECM) fungi, soil contamination caused a reduction of hyphal development in holm oak. However, our results indicate that TE in soil do not affect root fungal Shannon diversity, richness or guild abundance underneath wild olive and stone pine plants. Finally, the edible fungal sporocarps studied in the GCC presented bioaccumulation of Cu, Zn, and, especially, Cd.