Microbial respiration and biomass in soil of a lodgepole pine stand acidified with elemental sulphur

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Abstract
A study was conducted to determine the effects of elemental sulphur (So) dust pollution on pH, microbial respiration and biomass, glucose mineralization dynamics, and selected soil chemical characteristics in the organic and mineral soil of a Pinuscontorta Dougl. stand near Rocky Mountain House, Alberta. Six sampling sites were established 50 to 750 m downwind of a So block located at a sour gas processing facility. The sites represented a gradient in sulphur (S) concentrations (1072 to 35 800 μg•(g soil)−1) and pH (4.9 to 1.6). In the organic horizon, So dust significantly reduced the pH from a mean of 4.1 to 2.3 and microbial biomass from 753 to 130 mg C•(100 g dry weight soil)−1. Increasing acidification also reduced total Ca, Mg, K, Mn, and P. A reduction in the cations, P, and microbial biomass was particularly evident at a soil pH below 3.3. Glucose mineralization patterns were altered as a result of acidification. The time required by the soil microbial biomass to attain maximum CO2 efflux following glucose enrichment increased from 11 h in the least acidified soil (pH 4.1) to 38 h in the most acidified soil (pH 2.3). Soil respiration was not significantly affected by soil acidification. Microbial biomass was highly correlated with pH. The mineral soil demonstrated a decreasing trend in pH (5.0 to 3.7) with increasing S levels (79 to 499 μg•(g dry weight soil)−1), but no significant effects on respiration and biomass were detected. However, glucose utilization patterns revealed a tendency towards a slower responding and less efficient biomass with increasing acidity. The time to reach maximum CO2 efflux following glucose enrichment increased from 14 h in the least acidified site (pH 5.0) to 26 h in the most acidified site (pH 3.7). The use of biomass measurements coupled with glucose utilization patterns for providing insight into the effects of pollutant stress on soil microorganisms is discussed.

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