The influence of acid irrigation and liming on the soil microbial biomass in a Norway spruce (Picea abies [L.] K.) stand

Over a period of three years (1990–1992) microbial biomass-C (Cmic), CO2 evolution, the Cmic:Corg ratio and the metabolic quotient for CO2 (qCO2) were determined in a Norway spruce stand (Höglwald) with experimentally acid-irrigated and limed plots since 1984. A clear relationship between soil pH and the level of microbial biomass-(Cmic) was noted, Cmic increasing with increasing soil pH in Oh or Ah horizons. More microbial biomass-C per unit C{org} (Cmic:Corg ratio) was detected in limed plots with elevated pH of Oh or Ah horizons as compared to unlimed plots with almost 3 times more Cmic per unit Corg in the limed Oh horizon. Differences here are significant at least at the p=0.05 level. The positive effects of liming (higher pH) on the Cmic:Corg ratio was more pronounced in the upper horizon (Oh)). The total CO2 evolution rate of unlimed plots was only half of that noted for limed plots which corresponded to the low microbial biomass levels of unlimed plots. The specific respiratory activity, qCO2, was similar and not significantly different between the unlimed control plot and the limed plot.