Recovery of soil microbial biomass and activity from prescribed burning

Abstract

Development of humus layer soil microbial biomass C (C mic ) and N (N mic ), fungal biomass (as soil ergosterol content), microbial respiration activity, and the soil organic C (C org ) and N (N tot ) were determined in coniferous forest soils that had received a single prescribed fire treatment at different times over a period of 45 years. The ratio of soil respiration rate to microbial biomass C (qCO 2 ) and the C mic /C org and N mic /N tot percentages were derived from the measurements taken. All the measured biomass indicators reacted identically to show recovery from prescribed burning within 12 years. A raised metabolic quotient (qCO 2 ) was detected in soils over the first 2 years following the fire treatment, but after the third year it had decreased to a stable level. These observations suggest that during the first few years after fire the soil microflora can be characterized on the basis of simple substrate–decomposer relationships. The first 12 years were characterized by increasing C mic /C org and N mic /N tot percentages, which then stabilized at mean values of 1.3 and 5.5%, respectively. The observed rise in the C mic within a large pool of C org suggested increasing availability of energy-rich C sources. These C sources are probably derived from the organic C input resulting from postfire plant succession.