Plant growth promoting effect of selected autochthonous microorganisms (bacteria, yeast and/or arbuscular mycorrhizal fungi) in a heavy metals multicontaminated soil

Abstract

As plant (clover) development was limited in a heavy metal muIticontaminated soil the effect of selected autochthonous microorganisms as bacteria (B), yeast (Y) and arbuscular mycorrhizal (AM) fungi used either as single or dual inoculants, were assayed to ascertain whether these microbial treatment can benefit plant growth, nutrient uptake, and metal translocation . The inoculated microorganisms increased shoot biomass by 148% (B), 162% (Y) and 204% (AM), and root growth, partic!llarly in dual associations, and decreased metals translocation from soil to shoots. Dual inoculations also produced the highest symbiotic (AM colonization and nodulatíon) rates. The plant growth effect and the metal sequestration or bioaccumulation abilities demonstrated by these microorganisms seem to be involved in such effects. The activity of microbial antioxidant enzymes such as superoxide dismutase (SOD), catalase (CAT), glutattion reductase (GR) and ascorbate peroxidase (APX) known to play important roles in cell protection again abiotic stress, changed slightly in the culture medium of the bacteria or yeast in presence of metals. Such activities alleviate cellular oxidative damage, which is an important protective mechanism against heavy metal stress. These results are an indication of adaptation to high metal concentratíon of these autochthonous microorganisms. Thus, theYlIlay be consídered as an index of microbial metal tolerance. Microbial inoculations showed a bioremediation effect since reduced shoot metal concentration and increased nutrient in plants allowing growth developments and helping plant recovery of the multicontaminated soil. Therefore, the tested mycorrhizosphere interaction could be used as an environmental biotechnology tool for improving plant developments in heavy metal-contaminated environments.