Structure and function of the soil microbial community in microhabitats ofa heavy metal polluted soil

Particle-size fractionation of a heavy metal polluted soil was performed to study the influence of environmental pollution on microbial community stru cture, microbial biomass, microbial residues and enzyme activities in micro habitats of a Calcaric Phaeocem. In 1987, the soil was experimentally conta minated with four heavy metal loads: (1) uncontaminated controls; (2) light (300 ppm Zn, 100 ppm Cu, 50 ppm Ni, 50 ppm V and 3 ppm Cd); (3) medium; an d (4) heavy pollution (two- and threefold the light load, respectively). Af ter 10 years of exposure, the highest concentrations of microbial ninhydrin -reactive nitrogen were found in the clay (2-0.1 mum) and silt fractions (6 3-2 mum), and the lowest were found in the coarse sand fraction (2,000-250 mum). The phospholipid fatty acid analyses (PLFA) and denaturing gradient g el electrophoresis (DGGE) separation of 16S rRNA gene fragments revealed th at the microbial biomass within the clay fraction was predominantly due to soil bacteria. In contrast, a high percentage of fungal-derived PLFA 18:2 o mega6 was found in the coarse sand fraction. Bacterial residues such as mur amic acid accumulated in the finer fractions in relation to fungal residues . The fractions also differed with respect to substrate utilization: Urease was located mainly in the <2 <mu>m fraction, alkaline phosphatase and aryl sulfatase in the 2-63 mum fraction, and xylanase activity was equally distr ibuted in all fractions. Heavy metal pollution significantly decreased the concentration of ninhydrin-reactive nitrogen of soil microorganisms in the silt and clay fraction and thus in the bulk soil. Soil enzyme activity was reduced significantly in all fractions subjected to heavy metal pollution i n the order arylsulfatase >phosphatase >urease >xylanase. Heavy metal pollu tion did not markedly change the similarity pattern of the DGGE profiles an d amino sugar concentrations. Therefore, microbial biomass and enzyme activ ities seem to be more sensitive than 16S rRNA gene fragments and microbial amino-sugar-N to heavy metal treatment.