EFFECTS OF HEAVY-METAL CONTAMINATION ON THE SHORT-TERM DECOMPOSITION OF LABELED [C-14] GLUCOSE IN A PASTURE SOIL

The influence of heavy metal contamination on the efficiency of conver sion of fresh substrates into new microbial biomass in a pasture soil was examined. Three soils covering a range of chromium, copper and ars enic concentrations, and an uncontaminated control soil, were amended with [U-C-14]glucose and incubated for 28 days. During incubation, mic robial biomass C-14 was determined using the fumigation-extraction tec hnique. The amounts of (CO2)-C-14 evolved during incubation were monit ored, and residual C-14 concentrations were determined. Throughout the incubation, the microbial biomass-C-14 formed following addition of g lucose was consistently lower in the metal-contaminated soils than in the uncontaminated control soil. Soils differed significantly in their rates of (CO2)-C-14 evolution. More glucose-derived (CO2)-C-14 was ev olved from contaminated soil than from the uncontaminated control. The ratio of both (total respired C):(total biomass-C) and (respired (CO2 )-C-14:(biomass-C-14) was greater in the contaminated soils than in th e uncontaminated soil. The results suggest that the microbial biomass in soils contaminated with heavy metals are less efficient in the util ization of substrates for biomass synthesis and need to expend more en ergy for maintenance requirements.