Microbial recolonization and chemical changes in a soil heated at different temperatures

Samples of a Mediterranean forest soil were exposed in a muffle furnace to seven temperatures ( 100-700 degrees C) for 15 min to simulate different fire intensities. Heated soils were incubated for 100 days after re-inoculation with fresh unheated soil. Immediately after heating, the extractable organic C increased with the heating temperature, reaching a maximum at 400 degrees C. This increase in extractable organic C and nutrients in soils heated below 400 degrees C allowed a rapid recolonization of bacteria, increasing the basal respiration. During the 100-day incubation, the cumulative values of basal respiration and carbon mineralization rates generally followed a double exponential equation in unheated and heated samples. Heating at 200 degrees C caused a reduction of 99.6% for fungi ( measured as culturable fungal propagules), which showed lower recolonization capacity than that of bacteria. Heating also caused a decrease in the organic C content of the soils, especially for the highest temperatures. As a consequence, the microbial biomass carbon recovery was short lived in heated soils. The varied effects of heating and incubation on the inorganic and organic nitrogen changes, available nutrients and metabolic quotients are also discussed. This study demonstrates that changes in soils exposed to comparatively high temperatures (> 500 degrees C) have a particularly strong impact on microbial population.