Different sources of heavy metals and their long-term effects on soil microbial properties

We analysed soils of Lower Saxony, Germany, variously contaminated with sew age sludge, sediment, and dump material from mining and factory residues, t o assess the effects of different sources of heavy metals and different met al species (total, EDTA and NH4NO3 extractable) on activity (basal respirat ion), biomass (microbial C, adenylates) and community structure (ergosterol ) of soil microorganisms in relation to important chemical soil properties. The contents of biomass C adenylates and ergosterol did not necessarily de crease with increasing heavy metal content, reflecting the importance of ot her environmental factors, e.g. differences in C input. The biomass C/soil C ratio ranged from 0.19 to 2.10% and decreased in the order: sludge > sedi ment > dump contamination, in accordance with the increasing heavy metal lo ad. The ergosterol/biomass C ratio, which in contrast increased in the orde rs/sludge < sediment < dump contamination, varied between 0.45% and 3.10% a nd was on average 1.09%, i.e. it was much higher than in uncontaminated soi ls, indicating a change in community structure towards fungi. This ergoster ol/biomass C ratio was most markedly affected by the concentration of NH4NO 3-extractable Pb. The adenylate energy charge, ranging from 0.49 to 0.79, w as mainly affected by the three Cu species and showed a strong positive cor relation with the metabolic quotient qCO(2). The average ATP/biomass C rati o was 7.9 mu mol g(-1) biomass C. It was the only ratio that remained unaff ected by any of the soil properties or heavy metal species.