Implementation of (aided)phytoextraction in Pb/Zn mine tailings using hyperaccumulators improves soil health

Phytoextraction is a soil remediation technique that involves growing plants capable of absorbing and accumulating high levels of trace metals in their aboveground parts from contaminated soils. The process can be aided by the use of organic amendments or the intercropping of plants. A field trial of (aided)phytoextraction was implemented in an abandoned Pb/Zn-mining area in the NW of Spain. The Cd/Zn-hyperaccumulator Noccaea caerulescens was planted in monoculture or co-cropped with the leguminous Lotus corniculatus in replicate plots established in non-amended or compost-amended mine tailings. Compost amendment improved soil properties such as total C and N contents, C/N ratio and nutrient availability, but decreased soil metal availability. Compost addition improved plant nutrition and biomass production of the hyperaccumulator. After 1.5 years of plant growth, no significant changes in soil total metal concentrations were observed. However, the concentrations of NH₄Cl-extractable Zn decreased in plots cultivated with N. caerulescens. Intercropping with the legume induced significant increases in shoot metal concentrations in the hyperaccumulator. Both plant cover and compost addition increased the activity of hydrolytic and dehydrogenase enzymes, while decreasing catalase activity, which showed abnormally high values in mine tailings. The successful establishment of plant cover was essential to maintaining the improvement of organic matter and other soil properties induced by the compost amendment over time.