MICROBIAL BIOMASS IN SUBURBAN ROADSIDE SOILS - ESTIMATES BASED ON EXTRACTED MICROBIAL-C AND ATP

The effect of roadside metal contamination on the size of the soil microbial biomass was examined in soils from five roadside sites in S.W. London. The soils were predominantly light textured and soil pH ranged from a mean of pH 7.1 at 0.5 m from the road to pH 5.0 at 10 m from the road. Biomass-C, determined by the fumigation-extraction method, and soil ATP were measured at 0.5 and 10 m from the road where toxic metal concentrations in the soil were high and low, respectively. The mean biomass-C at 0.5 and 10 m from the road was 951 mug biomass-C g-1 soil and 740 mug biomass-C g-1 soil, respectively. There was no evidence that increased soil concentrations of Pb, Cu, Ni, Zn and Cd close to the road had adversely affected biomass size and the larger biomass at 0.5 m was attributed to a positive response to the higher soil pH and carbon levels measured at this distance. A larger CHCl3-extractable soil carbon fraction was measured in 0.5 m soil by Soxhlet analysis and was attributed to hydrocarbon contaminants from vehicle exhausts and road surface materials. The mean ratio of soil ATP to extracted microbial carbon was the same for 0.5 and 10 m soils and the mean ATP content of the biomass was 8.8 +/- 0.55 mumol ATP g-1 biomass-C. This provided some evidence that differences in hydrocarbon contamination between distances from the road had not affected the fumigation-extraction biomass-C measurements.