Elevated CO₂ enhances mycorrhizal inoculation efficiency in phytostabilization of a heavy metal-contaminated soil using Nicotiana glauca

Abstract

Elevated atmospheric CO₂ levels can influence the effectiveness of phytostabilization assisted by soil microorganisms in metal-contaminated soils. This study evaluated the efficacy of the native AM fungus Funneliformis mosseae in the establishment (3 months) of seedlings of the invasive species Nicotiana glauca R. C. Graham in a semiarid soil contaminated by several heavy metals (HMs), under ambient and elevated levels of CO₂ (420 vs. 760 ppm, respectively) and without fertilizer treatment. Thus, we tested the effect of this native AM fungus on the plant growth parameters, the percentage mycorrhizal colonization of roots, bioavailability of HMs in soil, accumulation of HMs in plant, soil structural stability, and the functions of microbial communities (soil enzyme activities) in the rhizosphere of N. glauca in response to elevated CO₂. The mycorrhizal inoculation with F. mosseae and elevated CO₂ increased synergistically the shoot (about 150 %) and root (about 53 %) dry biomass and shoot P content of N. glauca. Mycorrhizal inoculation was effective in reducing the bioavailability of toxic HMs in the soil, particularly Cd, Cu, and Zn, as well as shoot Cu uptake, and resulted in shoot bioconcentration factors for all metals lower than 1, regardless of the atmospheric CO₂ level. Meanwhile, the native AM fungus increased soil biomass C content, dehydrogenase, protease, and alkaline phosphomonoesterase activities, soil aggregate stability, and extractable K. In conclusion, this approach reduces metal mobility and improves soil microbial functioning and structural stability, enhancing long-term soil recovery in climate-stressed mining areas.

Keywords: Arbuscular mycorrhizal fungi; Heavy metals; Phytostabilization; Soil functionality.