Changes of Microbial Indices of Inoculated Fungi and Bacteria at Hyoscyamus niger L. Rhizosphere at Different Levels of Soil Lead (Pb) Pollution

Microorganisms are one of the important parts of soil, that their activity and population can be affected by the high levels of heavy metals such as lead (Pb). The objective of this study was to evaluate the changes of Microbial Indicators of inoculated fungi and bacteria in Hyoscyamus niger rhizosphere at different levels of lead (Pb). For this purpose, a soil was selected and various levels of Pb (0, 250, 500 and 1000 mg Pb kg-1 soil) were uniformly added to the soil. Then soil was sterilized and after soil inoculation with the mycorrhizal fungi (a mixture of Glomus intraradices, Funneliformis mosseae and Glomus fasciculatum species) and bacteria (species of Pseudomonas including P. putida, P. fluorescens, and P. aeruginosa), Hyoscyamus (Hyoscyamus niger L.) was grown. This study was carried out under greenhouse condition as a factorial experiment based on a randomized complete block design and in three replications. Results showed that increasing of Pb levels at soil, led to a significant (P≤ 0.05) reduction in the amounts of root colonization (41.1 percent), soil bacterial population (52.8 percent), soil microbial respiration, substrate induced respiration and microbial biomass carbon. While the metabolic quotient was not change significantly (P≤ 0.05). The maximum and minimum of changes (at Pb1000 compared to Pb0) were observed in microbial biomass carbon at bacteria inoculation (83.0 percent) and metabolic quotient at fungi inoculation (18.9 percent), respectively. The amount of microbial biomass carbon in fungi treatment was greater (1.28-2.62 times) than that in bacterial treatment. Results of this study indicated high sensitivity of bacteria on high levels of soil Pb contamination as well as higher tolerance of the fungi.