Effects of fresh and aged copper contaminations on soil microorganisms

The aim of the investigation was to compare effects of fresh and aged amendments of copper (Cu) on the active, aerobic, heterotrophic microbial biomass by respiration and potential‐nitrification measurements and on microbial‐community structure by means of phospholipid‐fatty‐acid (PLFA) analyses. An A_p horizon (10–20 cm) of a Luvisol was used for the experiments. Fresh copper amendments were carried out by spraying a CuCl₂ solution on the soil. Aged heavy‐metal amendments were achieved by mixing the control soil with monocontaminated soil derived from an abandoned site in Denmark which has been used as a wood‐preservation plant. As expected, fresh contaminations were more effective to reduce potential nitrification and respiration than aged contaminations if the total Cu concentration (Cu_t) in soils is considered. There were no differences between aged and fresh contaminations if their effects were referred to NH₄Cl‐extractable concentrations (Cu_AN). The lowest concentration reducing cumulative substrate‐induced respiration (C_R) amounted to 0.33 mg Cu_AN (kg dm)^–1. PLFA analyses revealed Cu contaminations to decrease mainly aerobic bacteria. Effects were more pronounced using the contaminated soil as an inoculum. Apparently the duration of contamination is more important to the change of microbial‐community structure than the actual availability of the contaminant.