The influence of arbuscular mycorrhizal (AM) fungi (Glomus intraradices) and of heavy metal stress on the characteristics of biomass production, as well as non-enzymatic and enzymatic variables in the roots, shoots, and leaves of sunflower (Helianthus annuus L.) plants were studied at pot and field scales. The intensity of the mycorrhizal colonization (M%) and the arbuscular abundance in the root system (A%) were found to be higher in the sunflower grown at lab scale (artificially inoculated) than that grown at field scale (natively inoculated). Thus, the AM symbiosis with the sunflower root system exposed to a different degree of pollution had a differential protective effect on plants at lab and field scales. A huge biomass of sunflower was harvested from the field compared to that obtained from the lab experiment. Furthermore, after measuring the biochemical variables of the plant parts, the results indicated a decrease in field for the superoxide dismutase and peroxidase activity, for the lipid peroxidation content, and for the assimilating pigments, while all quantified variables showed almost the same pattern of variation in all three plant parts. Consequently, it can be concluded that it is possible to use biochemical response variables, which in the case of our study are consistent with the protective effect of the fungus, as environmental biomarkers for soils with moderate pollution.