Helichrysum microphyllum subsp. tyrrhenicum, Its Root-Associated Microorganisms, and Wood Chips Represent an Integrated Green Technology for the Remediation of Petroleum Hydrocarbon-Contaminated Soils

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

Metal phytostabilization by mastic shrub (Pistacia lentiscus L.) and its root-associated bacteria in different habitats of Sardinian abandoned mining areas (Italy)

Pistacia lentiscus L. is an excluder metallophyte proposed for the revegetation and phytostabilization of metal-contaminated sites in the Mediterranean area. The present study aims at evaluating the linking between bacterial communities and plants spontaneously growing in ecosystems chronically impacted by mining activities. Environmental properties and metal accumulation into hypogeal and epigeal tissues were analyzed in wild plants of two contrasting habitats with extreme metal contamination (> 2300 mg/kg for Zn, > 1100 mg/kg for Pb, > 10 mg/kg for Cd). The community structures of rhizospheric and root endophytic bacteria were fingerprinted by terminal restriction fragment length polymorphism of the 16S rRNA gene. The wild shrubs efficiently restrict the accumulation of the three major contaminants to the epigeal tissues in the two habitats under study (249 +/- 68 mg/kg dw for Zn, 43 +/- 21 mg/kg dw for Pb, and 1.4 +/- 0.5 mg/kg dw for Cd). Evidence was provided that the combined but not individual effect of environmental conditions (moisture, inorganic carbon, pH) and proportion between Zn and Cd in the mine substrate play a role in structuring rhizosphere bacterial communities. The observed changes in community structures of root endophytes were found to be strongly associated with Pb level in roots and substrate properties (inorganic carbon and Zn/Cd ratio). Overall, our study highlights the importance of the analysis of multifactorial interactions among mine substrate, plant, and microbes for understanding how the environmental context affects phytoremediation under real conditions