SOIL P STATUS AND PHOSPHOMONOESTERASE ACTIVITY OF RECENTLY BURNT AND UNBURNT SOIL FOLLOWING LABORATORY INCUBATION

The effects of laboratory incubation on P form distribution and phosph omonoesterase activity in a forest soil recently affected by a wildfir e (B) were compared with its effects on these properties of an unburnt soil from an adjacent plot (UB). Samples of surface (0-5 cm) and subs urface (5-10 cm) layers of both soils were incubated at 75% field capa city and 28 degrees C for 11 wk. After 0, 1, 2, 4, 6 and 11 weeks, sam ples were withdrawn and fractionated and the P contents of fractions f rom corresponding layers were compared. The 0-5 cm layer was most seve rely affected by the fire, which caused oxidation of organic P (P-o) a nd a marked decrease in the content of residual P (P-r). The major pro cess occurring during the incubation of this layer was microbial immob ilization of inorganic P (P-i) in organic forms. By contrast, the 5-10 cm layer behaved similarly to the UB soil during incubation: essentia lly, P-r was transformed into rapid turnover P-o (NaHCO3-extractable P -o + NaOH-extractable P-o), and P-i was occluded. After destruction of the enzyme due to burning, both layers of the B soil exhibited a very low initial rate of phosphomonoesterase activity. The failure of the enzyme activity to increase during incubation coincided with high labi le P-i concentrations, suggesting that microbial synthesis of new phos phomonoesterase enzyme was repressed. (C) 1998 Elsevier Science Ltd. A ll rights reserved.