MICROBIAL CARBON TURNOVER IN BEECH FOREST SOILS AT DIFFERENT STAGES OF ACIDIFICATION

Microbial carbon turnover was investigated in six beech forest soils (0-10 cm). The soils were sampled in the Gottinger Wald area (Germany) and had developed under identical environments (climate, topography, vegetation) but from different parent materials. The pH-H2O of the soils was in the range between 4.8 and 8.3. The content of soil organic C was positively related to factors indicating soil acidification and decreased from 96.6 mg C g-1 dry wt in the soil with the highest amount of exchangeable Ca to 31.3 mg C g-1 dry wt in the soil with the lowest amount of exchangeable Ca. The size of the microbial C pool varied between 0.70 and 1.52 mg C g-1 soil, the metabolic quotient qCO2 varied between 1.4 and 2.4 mg CO2-C g-1 biomass C h-1. Exchangeable Ca was positively correlated to the biomass of the microflora and to the microbial incorporation of C from freshly fallen litter. In contrast, exchangeable Ca was negatively correlated to the C(biomass):C(org), ratio, to C mineralization rate, to qCO2 and to the specific death rate (qD). It was concluded that the small but metabolically-active microflora in the more acid soils has a reduced ability to incorporate C from freshly fallen litter into the subsurface C cycle and may thus partly be responsible for the low content of organic C in these soils.