Trifolium repens-Associated Bacteria as a Potential Tool to Facilitate Phytostabilization of Zinc and Lead Polluted Waste Heaps

Abstract

Heavy metals in soil, as selective agents, can change the structure of plant-associated bacterial communities and their metabolic properties, leading to the selection of the most-adapted strains, which might be useful in phytoremediation. Trifolium repens, a heavy metal excluder, naturally occurs on metal mine waste heaps in southern Poland characterized by high total metal concentrations. The purpose of the present study was to assess the effects of toxic metals on the diversity and metabolic properties of the microbial communities in rhizospheric soil and vegetative tissues of T. repens growing on three 70–100-years old Zn–Pb mine waste heaps in comparison to Trifolium-associated bacteria from a non-polluted reference site. In total, 113 cultivable strains were isolated and used for 16S rRNA gene Sanger sequencing in order to determine their genetic affiliation and for in vitro testing of their plant growth promotion traits. Taxa richness and phenotypic diversity in communities of metalliferous origin were significantly lower (p < 0.0001) compared to those from the reference site. Two strains, Bacillus megaterium BolR EW3_A03 and Stenotrophomonas maltophilia BolN EW3_B03, isolated from a Zn–Pb mine waste heap which tested positive for all examined plant growth promoting traits and which showed co-tolerance to Zn, Cu, Cd, and Pb can be considered as potential facilitators of phytostabilization.

Coronilla juncea, a native candidate for phytostabilization of potentially toxic elements and restoration of Mediterranean soils

“…The tolerance of C. juncea to PTE might be linked to its root symbiosis with nitrogen-fixing bacteria as previously reported for other leguminous 56 , 57 . Our data sustain this idea by the higher number of nodules in root parts of plants located in the contaminated area.…”

Heavy Metal Tolerance and Accumulation Potential of Coastal Accessions of Trifolium Fragiferum, a Promising Forage Species

“…There is no doubt that cultivation of T. fragiferum in heavily metal-contaminated soils will leed to accumulation of these heavy metals in above ground parts well above permissable levels. However, both heavy metal tolerance and accumulation potential in natural conditions can be significantly affected by symbiosis with arbuscular mycorrhiza and associated rhizobacteria, as in the case of T. repens (Oleńska et al 2020;Xiao et al 2020;Xiao et al 2021) and T. pratense (Vivas et al 2003).…”

Phytoremediation Potential of Native Herbaceous Plant Species Growing on a Paradigmatic Brownfield Site

“…For instance, plant species belonging to the Leguminosae family, such as Medicago lupulina, Lotus corniculatus, and Trifolium repens, were reported to make major contribution to phytostabilization (Amer et al, 2013;Bert et al, 2000;Bidar et al, 2007), whereas only Medicago lupulina showed some Pb translocation ability to aerial parts (Amer et al, 2013). The tolerance of Trifolium repens to contaminated sites should also be noted, with the roots being the main organ of Pb accumulation (Bidar et al, 2007;Oleńska et al, 2020). In another study, Lotus corniculatus showed the bioaccumulation of PTEs not exceeding current legal limits for Cd, Cr, and Pb.…”