Practical evaluation of carbon sources of forest soils in Slovenia from stable and radio-carbon isotope measurements

Carbon sources were estimated by measuring carbon isotope ratios (δ13C and Δ14C) with accelerator mass spectrometry (AMS) in forest soils of different lithology. Six locations were selected in temperate deciduous and coniferous stands in Slovenia (Žirovski vrh, Idrija, Kocevski Rog, Pohorje, Gorisnica, and Rakitna), where carbonate rocks consisting of limestone and dolomite are abundant as underlying bedrock. Carbon isotope fractionation would not have occurred in two carbonaceous soils, since the values of both δ13C and Δ14C changed consistently in these soils after thermal (550°C, 2 h) or chemical (1 M HCl, 24 h) treatments. Organic components were found to be predominant carbon sources (70–100%) in the uppermost portions (0–2 cm in depth). In deeper portions at a depth of about 30–35 cm, soil carbon may be derived completely from underlying carbonate minerals in Idria, western part of Slovenia. The Combination of heat and chemical treatments with AMS provides practical information on soil carbon sources in carbonaceous soils.