RECOVERY OF SOIL MICROBIAL BIOMASS AND ACTIVITY FROM PRESCRIBED BURNING

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 (qCO2) 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 (q CO2) 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.