Relationship between soil organic carbon and microbial biomass on chronosequences of reclamation sites

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Abstract
The interrelationship between soil microorganisms and soil organic carbon was studied on an agricultural and on a forest chronosequence of open-pit mine reclamation soils. Thirty years after reclamation, soil carbon levels of 0.8% on the agricultural sites and 1.7% on the forest sites (A-horizon) were reached. Microbial biomass rose very fast to levels characteristic of undisturbed soils. Microbial carbon (Cmier) was 57 mg·100 g−1 soil after 15 years on the agricultural sites and 43 mg·100 g−1 on the forest sites. The contribution of Cmier to the total organic carbon (Corg) decreased with time, more rapidly on the forest sites than on the agricultural ones. From the Cmierr/Corg ratio it became evident that both chronosequences had not yet reached a steady state within the 50 years of reclamation. A significant decrease of the metabolic quotient qCO2 (microbial respiration per unit biomass) with time was observed on the agricultural sites but not on the forest sites. The Cmier/Corg ratio proved to be a reliable soil microbial parameter for describing changes in man-made ecosystems. For evaluating reclamation efforts, the Cmier/Corg ratio can be considered superior to its single components (Cmier or Corg) and to other parameters.