An Evaluation of Some Soil Biological Indices in the Presence of Growth-Promoting Rhizobacteria and when Soil Contamination with Cd

Cadmium effects on soil microbial indices and on the interaction of Arbuscular Mycorrhiza Fungi (AMF) and as well on Plant Growth Promoting Rhizobacteria (PGPR) were investigated. The experiments were performed in the framework of a factorial design with levels of cadmium (0، 10، 30 and 100 mg kg-1 soil)، and microbial inoculations (Control، PGPR and AMF) employing Russian Kanapweed as the experimental plant. The experiments were triplicated. The results indicated that soil Cd pollution caused significant decline in plant growth، microbial respiration، Substrate Induced Respiration (SIR)، Carbon Availability Index (CAI)، Microbial Biomass Carbon (MBC) as well as microbial population. In PGPR and AMF treatments، MBC decreased respectively by 57 and 60% as compared with control (Cd0). Cd addition significantly increased qCO2، this index being 22% higher in Cd100 as compared with Cd0. The results indicated that Cd exerts toxic and inhibitory effects on soil microbial activity even at low concentrations. Nonetheless a presence of growth-promoting microorganisms could decline the inhibitory effects of cadmium against plant growth and as well against soil biological activities.