WOOD-ASH FERTILIZATION AND FIRE TREATMENTS IN A SCOTS PINE FOREST STAND - EFFECTS ON THE ORGANIC LAYER, MICROBIAL BIOMASS, AND MICROBIAL ACTIVITY

We studied the reactions of humus layer (F/H) microbial respiratory ac tivity, microbial biomass C, and the fungal biomass, measured as the s oil ergosterol content, to the application of three levels of wood ash (1000, 2500, and 5000 kg ha(-1)) and to fire treatment in a Scots pin e (Pinus sylvestris L.) stand. Physicochemical measurements (pH, organ ic matter content, extractable and total C content, NH4+ and total N c ontent, cation-exchange capacity, base saturation) showed similarity b etween the fire-treated plots and those treated with the lowest dose o f wood ash (1000 kg ha(-1)). The ash application did not change the le vel of microbial biomass C or fungal ergosterol when compared to the c ontrol, being around 7500 and 350 mu g g(-1) organic matter for the bi omass C and ergosterol, respectively. The fire treatment lowered the v alues of both biomass measurements to about half that of the control v alues. The fire treatment caused a sevenfold fall in the respiration r ate of field-moist soil to 1.8 mu l h(-1) g(-1) organic matter compare d to the values of the control or ash treatments. However, in the same soils adjusted to a water-holding capacity of 60%, the differences be tween the fire treatment and the control were diminished, and the ash- fertilized plots were characterized by a higher respiration rate compa red to the control plots. The glucose-induced respiration reacted in t he same way as the water-adjusted soil respiration. The metabolic quot ient, qCO(2), gradually increased from the control level with increasi ng applications of ash, reaching a maximum in the fire treatment. Nitr ification was not observed in the treatment plots.