How autochthonous microorganisms influence physiological status of Zea mays L. cultivated on heavy metal contaminated soils?

The aim of this study was to investigate the effect of autochthonous microorganisms present in soil collected from heavy metal (HM) uncontaminated (Pb ≈ 59 mg kg−1, Cd ≈ 0.4 mg kg−1, Zn ≈ 191 mg kg−1), moderately (Pb ≈ 343 mg kg−1, Cd ≈ 12 mg kg−1, Zn ≈ 1876 mg kg−1), and highly (Pb ≈ 1586 mg kg−1, Cd ≈ 57 mg kg−1, Zn ≈ 3280 mg kg−1) contaminated sites on Zea mays elemental composition, physiological status, and growth parameters. For this purpose, half of the collected soil was sterilized and soil characterization was performed. After 45 days of cultivation, the presence of HM in the soil negatively affected photosynthesis and transpiration rates, relative chlorophyll content, anthocyanins index, chlorophyll fluorescence parameters, and content of oxidative stress products (H2O2 and Malondialdehyde) of Zea mays, while soil sterilization had a positive effect on those parameters. Average percentage of colonization of root segments by arbuscular mycorrhiza fungi decreased with an increase of HM contamination in the soil. The increase in shoot concentration of HMs, particularly Cd and Zn, was a result of contaminated soils sterilization. Aboveground biomass of maize cultivated on sterilized soil was 3-fold, 1.5-fold, and 1.5-fold higher for uncontaminated, moderately contaminated and highly contaminated soils respectively when compared to nonsterilized soils. Contrary to our expectation, autochthonous microflora did not improve plant growth and photosynthetic performance; in fact, they had a negative effect on those processes although they did reduce concentration of HMs in the shoots grown on contaminated soils.