Phytomanagement of Zn and Cd Contaminated Soil: Helianthus Annuus Biomass Production and Metal Remediation Abilities With Plant Growth Promoting Microbiota Assistance

Abstract

Mining and industrial activity are contributing to the increase of heavy metal (HM) pollution in the environment, especially in soil. These metals leach into water, spread to plants and enter the food chain. Phytoremediation coupled to selected rhizosphere microbiota is an environmentally friendly technology designed to promote HM bioremediation in soils. In this study, sunflower ( Helianthus annuus L.) was used together with Rhizophagus irregularis, an arbuscular mycorrhizal fungi (AMF), and Cupriavidus sp. strain 1C2, a plant growth promoting rhizobacteria (PGPR), as a phytoremediation strategy to remove Zn and Cd from an industrial soil (599 mg Zn kg and 1.2 mg Cd kg ) and produce plant biomass - an agricultural soil was also used to obtain a H. annuus growth and metal accumulation control. The H. annuus biomass in the contaminated industrial soil was 17% lower, at harvest than that in an agricultural soil. Removals of ca. 0.04 and 0.91% of Zn and Cd respectively were obtained with the biomass produced in the industrial soil in a single crop. Bioaccumulation, remediation and translocation factors corroborated the higher Zn and Cd accumulation in the roots, compared to other plants parts. The survival of applied microbiota was indicated by a high root colonization rate of AMF and identification of strain 1C2 in the rhizosphere at the end of the phytoremediation assay. Changes in the bacterial community occurred in the industrial soil and were possibly associated to the phytoremediation effect on the rhizosphere: metals removal by the plant together with the synergic relationships established between AMF, PGPR and the autochthonous microbial community might have favoured specific soil bacterial genera, namely Nitrospira, Acidobacterium and Candidatus Koribacter. In this study, an optimized phytomanagement strategy applied to a real contaminated soil was successfully tested, and plant biomass with potential for upstream energetic valorisation purposes was produced.