Physiological response of Arizona cypress to Cd-contaminated soil inoculated with arbuscular mycorrhizal fungi and plant growth promoting rhizobacteria

Abstract

Increasing some industrial activities has been constantly contaminated the soil with different toxic metals leading to serious environmental concerns. However, some beneficial soil microorganisms would be useful tools for reducing toxic effects of heavy metals without producing toxic residuals. Therefore, present study was conducted to evaluate potential role of Pseudomonas fluorescens and arbuscular mycorrhizal fungi (AMF) in reducing cadmium toxicity in the Arizona cypress seedlings both individually and in combination. Factorial experiment was conducted based on a completely randomized design with three factors comprising AMF inoculation (Rhizophagus irregularis or Funneliformis mosseae or a mixture of both species, and non-inoculated controls), bacterial inoculation (P. fluorescens or Non-inoculated), and five levels of Cd (0, 5, 10, 15, and 20 mg kg−1) using three replications. Results of this study showed that, Arizona cypress growth decreased when exposed to high levels of Cd contamination. However, co-inoculation plants with all mycorrhizae and P. fluorescens grown under the highest levels of Cd contamination, showed increased photosynthetic pigments. Furthermore, AMF and P. fluorescens increased ascorbate peroxidase activity, which is responsible for the elimination of H2O2 when plants exposed to Cd stress. Moreover, high levels of Cd contamination negatively influenced phosphorus uptake by the plants, especially in control plants. Moreover, in seedlings inoculated with mycorrhizal fungi, accumulation of Cd was found to be less, apparently as a result of AMF modification of the influx of Cd into the host plants, as confirmed by reduced hydrogen peroxide and enhanced antioxidant enzyme activities compared to the control plants. AMF treatments increased glomalin related soil proteins concentration compared to the control plants. Also, the highest amount of glomalin production was observed in two species of Mix and FM. In conclusion, either co-inoculation with AMF and P. fluorescens or individual inoculation with AMF could potentially ameliorate harmful effects of Cd on Arizona cypress growth. .