PATTERN OF MICROBIAL INDICATORS IN FOREST SOILS ALONG AN EUROPEAN TRANSECT

Microbial biomass C and activity were determined in six forest soils a long a gradient in physical and chemical climate in Europe. Both param eters were measured microcalorimetrically. The upper 22 cm of the soil s were sampled in undisturbed columns (24 cm deep). Measurements were made in homogenized samples of the different surface organic horizons (Ol, Of, Oh) and the mineral horizons (Ah, Aeh, Bv) down to 22 cm. On a mass basis values for both the biomass and the activity showed an ex ponential decrease with depth in all soils. Expressed on a volume basi s these relationships varied with soil pH. In the strongly acidified s oils most of the microbial biomass and activity was located in the for est floor. In less acidified soils both parameters were highest in the mineral soil. Further relationships between biomass and activity and between soil chemical properties showed significant positive correlati ons with exchangeable Ca2+, Mg2+, Ca/Al and negative correlations with Al3+. There were no significant correlations with exchangeable cation s in less acidified soils. It was calculated that the microbial biomas s is more affected by soil chemistry than activity. The caloric quotie nt (qW) is a good parameter for determining the ecophysiological state of microorganisms in acidified soils.