Changes in Microbial Biomass Carbon, Ecophysiological indices, Basal Respiration and Substrate-Induced Respiration of Soil After Incubation with Different Lead Levels

Heavy metals have adverse effects on soil microbial ecology. Impact of heavy metals on microbial populations has been investigated worldwide. In this study، some microbial indices were determined to evaluate the negative effects of lead on soil health during the six-month incubation of soil with different levels of lead. Lead was added to the soil at rates of 0، 100، 200، 300، 400 and 500 mgkg-1 as Pb (NO3) 2. Microbial biomass carbon، basal respiration، substrate induced respiration and two ecophysiological indices (metabolic quotient and microbial quotient) were measured as the most sensitive biological indices of soil against the pollutant after incubation times of 3، 15، 30، 90 and 180 days. In initial days of incubation and in low levels of lead، substrate induced respiration was increased. But this index was decreased by the increment of lead pollution level. By increasing the incubation time، low levels of lead also decreased substrate induced respiration. At 180 days of incubation despite of decreasing in available carbon sources، increment in some of indices such as microbial respiration and microbial biomass carbon were observed as a result of community tolerance induction. Based on our results، Pb concentration range of 100-300 mgPbkg-1 soil can be considered as critical range of Pb for quality indices in this soil at which negative effect was markedly observed.