Phytoremediation and the use of suitable amendments are well-known technologies for the mitigation of petroleum hydrocarbon (PHC) contaminations in terrestrial ecosystems. Our study is aimed at combining these two approaches to maximize their favorable effects. To this purpose, Helichrysum microphyllum subsp. tyrrhenicum, a Mediterranean shrub growing on sandy and semiarid soils, was selected. The weathered PHC-polluted matrix (3.3 ± 0.8 g kg⁻¹ dry weight) from a disused industrial site was employed as the cultivation substrate with (WCAM) or without (UNAM) the addition and mixing of wood chips. Under the greenhouse conditions, the species showed a survival rate higher than 90% in the UNAM while the amendment administration restored the totality of the plant survival. At the end of the greenhouse test (nine months), the treatment with the wood chips significantly increased the moisture, dehydrogenase activity and abundance of the microbial populations of the PHC degraders in the substrate. Cogently, the residual amount of PHCs was significantly lower in the UNAM (3–92% of the initial quantity) than in the WCAM (3–14% of the initial quantity). Moreover, the crown diameter was significantly higher in the WCAM plants. Overall, the results establish the combined technology as a novel approach for landscaping and the bioremediation of sites chronically injured by PHC-weathered contaminations.

Mine tailings represent a large-scale issue requiring the development of a sustainable remediation management plan with a multifactorial approach. In the Iglesiente region, past mining activities left severe contamination of Zn, Pb and Cd. Among bioremediation technologies, phytoremediation appears to be a promising strategy owing to the use of autochthonous plant species and their associated microorganisms naturally adapted to these harsh conditions. Among phytoremediation strategies, phytostabilization takes place at the root-substrate interface, where excluder-type metallophytes and their root-associated microorganisms reduce metal mobility and bioavailability. The effectiveness of this process largely depends on the structure and function of the rhizospheric microbiome. Therefore, the study of microbiome in rhizosphere and roots of native plants is crucial for the development of a successful remediation strategy. In this study, we investigated the rhizosphere and root microbiomes of Pistacia lentiscus, a metallophyte autochthonous plant species of Sardinian mining areas. Furthermore, the environmental context was analysed with a multifactorial approach to understand the most suitable application of phytoremediation in real field conditions. Sampling was conducted in three zones based on proximity to a mine tailing deposit: outside, at the border, and inside the dump. A comprehensive insight into soil communities was achieved by using diverse techniques. In this study we analysed: i) physico-chemical properties of mine substrates, ii) microbial activity by the dehydrogenase assay, iii) functional diversity patterns of microbial community with the BIOLOG system, iv) bacterial and fungal communities by high-throughput sequencing of ribosomal genes. Metals levels in the tailings showed a certain degree of spatial heterogeneity. Dehydrogenase activity showed a marked and statistically significant differences in the functional diversity of the rhizospheric microbial communities from the three different investigated areas. Analysis of microbial community by high-throughput sequencing allow us to understand how microbial communities were affected by environmental conditions and metals. Our results highlight the importance of plant-associated microbiomes in metal-contaminated environments and support their relevance for site-specific remediation strategies. This work has been developed within the framework of the project e.INS www.einsardinia.eu (Next Generation EU- PNRR-M4 C2 I1.5 CUP F53C22000430001).

Among phytoremediation strategies, phytostabilization takes place at the root-substrate interface, where excluder-type metallophytes and their root-associated microorganisms reduce metal mobility and bioavailability. The effectiveness of this process largely depends on the structure and function of the rhizospheric microbiome. To better understand the factors influencing phytostabilization under real field conditions, a multifactorial approach is essential. In this study, we conducted an integrative analysis of the microbial diversity and enzymatic activity in the rhizosphere of Pistacia lentiscus, an excluder-type metallophyte naturally growing in a highly contaminated (Zn, Pb and Cd) mine tailing dump and in surrounding area. Our findings provide insights into the ecological role of root-associated microbiomes in metal-contaminated environments and support their relevance for site-specific remediation strategies.

Abandoned mines represent a major environmental concern worldwide, posing serious risks to human health and ecosystems. In this study, microbial abundance and dehydrogenase activity were evaluated in surface substrates collected from a highly contaminated (Zn, Pb and Cd) tailing dump and in the surrounding areas. The heterotrophic community inside the studied site was found to be severely impaired as compared to control sectors located at the border and outside the tailing dump. The analysis of the microbial community composition by sequencing of the ribosomal genes is currently in progress. Overall, the study will allow us to identify the microbial components most severely affected by the extreme environmental conditions present in the mine tailings.