CHANGES IN SOIL-PHOSPHORUS AND ACID-PHOSPHATASE-ACTIVITY IMMEDIATELY FOLLOWING FOREST-FIRES

Three soils affected by wildfires and a soil that had been subjected to a controlled fire were sampled at two depths (0-5 and 5-10 cm), between 1 day and 1 month after burning. In all cases an unburnt soil was used as a control. The controlled fire did not affect acid phosphatase activity and had only very slight effects on P fraction distribution, in good agreement with the low soil temperatures recorded during the fire (never > 50-degrees-C in the upper 5 cm of soil). On the other hand, wildfires strongly reduced acid phosphatase activity and had an intense mineralizing effect on organic P; consequently inorganic P greatly increased and P fractions distribution was profoundly altered. The reductions in acid phosphatase activity and the extent of organic P oxidation in the various soil samples were used to estimate the soil temperatures reached during each fire. We show that there is a close relationship between soil temperatures estimated in this way and changes in P distribution within the various inorganic and organic fractions.