Showing papers by "Richard D. Bardgett published in 1994"

Impact of pasture contamination by copper, chromium, and arsenic timber preservative on soil microbial properties and nematodes

Abstract: Microbial properties and nematode abundance were measured along a gradient of increasing Cu, Cr, and As concentrations (50–1300 mg Cr kg-1) in the top 5 cm of a pasture soil contaminated by runoff of preserving liquor from an adjacent timber-treatment plant. Microbial biomass C and N were significantly (P<0.05) lower in contaminated than uncontaminated soils. The amount of microbial biomass C as a percentage of total organic C declined significantly (r 2 value with Cr 0.726*) with increasing contamination, and the ratio of respired C to biomass C was significantly (P<0.05) higher with contamination. Substrate-induced respiration, microbial biomass P, and denitrification declined (r2 value with Cr 0.601, 0.833*, and 0.709*, respectively) with increasing contamination. Increasing contamination had no effect on prokaryote substrate-induced respiration but eukaryote: eukaryote substrate-induced respiration declined significantly (r 2 value with Cr 0.722*). Accordingly, the ratio of prokaryote substrate-induced respiration increased significantly (r 2 value with Cr 0.799*) with contamination. There was a significant (r 2 value with Cr 0.872*) hyperbolic relationship between sulphatase activity and contamination, with activity declining by approximately 80% at >1000 mg Cr kg-1. Increasing contamination had no effect on basal respiration, dimethyl sulphoxide reduction, and phosphatase, urease, and invertase activities. Numbers of plant-associated nematodes declined significantly (r 2 value with Cr 0.780*) with contamination. On a percentage basis, plant-feeding nematodes predominated in less contaminated soils, whereas bacterial-feeding and predatory nematodes predominated in heavily contaminated soils. The use of the fumigation—incubation procedure for measurement of microbial biomass C in heavy-metal contaminated soils is discussed.

Effects of heavy metal contamination on the short-term decomposition of labelled [14C]glucose in a pasture soil

Abstract: The influence of heavy metal contamination on the efficiency of conversion of fresh substrates into new microbial biomass in a pasture soil was examined. Three soils covering a range of chromium, copper and arsenic concentrations, and an uncontaminated control soil, were amended with [U-14C]glucose and incubated for 28 days. During incubation, microbial biomass 14C was determined using the fumigation-extraction technique. The amounts of 14CO2 evolved during incubation were monitored, and residual 14C concentrations were determined. Throughout the incubation, the microbial biomass-14C formed following addition of glucose was consistently lower in the metal-contaminated soils than in the uncontaminated control soil. Soils differed significantly in their rates of 14CO2 evolution. More glucosederived 14CO2 was evolved from contaminated soil than from the uncontaminated control. The ratio of both (total respired C): (total biomass-C) and (respired 14CO2): (biomass-14C) was greater in the contaminated soils than in the uncontaminated soil. The results suggest that the microbial biomass in soils contaminated with heavy metals are less efficient in the utilization of substrates for biomass synthesis and need to expend more energy for maintenance requirements.