Effect of fertilization, carbon-based material, and redmud amendments on the bacterial activity and diversity of a metal(loid) contaminated mining soil

Soil amendments can be used to improve phytoremediation of polluted soils. Little is known about the effects of single or combined amendment addition on the bacterial community. Two carbon-based amendments, a biochar and an activated carbon, and two redmuds were applied to a lead and arsenic contaminated mine spoil Technosol, alone or in combinations. The bacterial community was evaluated using enzyme activities, Biolog EcoPlates, and next-generation sequencing with reference to untreated soil and fertilized soil. Fertilization had a negative effect on the bacterial community diversity and activity. The two carbon-based materials decreased β-glucosidase activity but increased carbon-related activity (Biolog EcoPlates) while the two redmuds increased the overall activity of the bacterial community. The combination of biochar and redmud increased both the diversity and activity of the bacterial community. All treatments induced a shift in the bacterial community structure. The treatments containing the neutralized redmud and/or biochar clustered together, whereas the treatments with nonprocessed redmud and activated carbon were closer to nonamended soil, while the bacterial community of the fertilization treatment was different from it. Treatments with biochar and/or neutralized redmud resulted in a similar community composition while the bacterial community of the treatments with activated carbon and nonprocessed redmud remained more similar to that of the nonamended technosol.