The effect of extreme temperatures on soil organic matter decomposition from Atlantic oak forest ecosystems.

Summary This work designs a heatwave with a calorimeter to analyze the response of soils from oak forest ecosystems to increasing temperature from 20 to 60 oC and to cooling from 60 oC to 20 oC. Calorimetry measures the heat rate of the soil organic matter decomposition and the response to increasing and decreasing temperatures directly. It was applied to soil samples representing different soil horizons with organic matter at different degree of decomposition given by their heat of combustion, calculated by differential scanning calorimetry. Results showed temperature-dependent decomposition rates from 20 to 40 or 50 oC typical for enzymatic activity. From 40 to 60 oC changes in the rates are less predictable. Data analysis during cooling showed that all samples suffered losses of their enzymatic capacity and that only those with the heat of combustion values close to that of carbohydrates resisted the heat wave.