Soil heavy metal concentrations, microbial biomass and enzyme activities in a contaminated grassland ecosystem

Soil enzyme activities and microbial biomass were measured in a grassland ecosystem with a wide range of heavy metal concentrations ranging from 7.2 to 48.1 mmol kg−1 (As, Cd, Cr, Cu, Ni, Pb and Zn) in portions of the U.S. Armyʹs Aberdeen Proving Ground, Maryland, U.S.A. Total and fluorescein diacetate active (FDA) fungal biomass, FDA-active bacterial biomass, substrate-induced respiration (SIR), the activity of N-acetylglucosaminidase, β-glucosidase, endocellulase, and acid and alkaline phosphatases were also measured. Most measures of microbial biomass were lower in polluted soils. Significant reductions (10- to 50-fold) in the activities of all enzymes closely paralleled the increase in heavy metal concentrations. These results demonstrate that heavy metal contamination of soil has adversely affected the abundance and activity of microorganisms involved in organic matter decomposition and nutrient cycling in this site.