The use of carbon isotopes (13C,14C) in different soil types and vegetation coverage in a montane atlantic forest region, Southeast Brazil

The study of the paleoenvironment depends upon proxies of palaeovegetation associated with chronological records. Carbon stable isotopes in soil samples provide information on the past vegetation type due to differences in mass fractionation during photosynthesis. Radiocarbon measurements on soil organic matter may also have different behaviors, given the complexity of soils as mixtures of multiple sources. With the aim of investigating how different soils, under different vegetation coverages, may affect paleoenvironmental reconstructions, we have analyzed four soil profiles collected at the Itatiaia National Park, between Rio de Janeiro and Minas Gerais states in Brazil, in the context of the Atlantic Forest biome, at altitudes between 1898m and 2457m. Different chemical fractions of the bulk soil were separately C-14 dated for each sample depth. For the total soil and the non-hydrolyzable carbon, discrepancies in pMC values were mostly within 5% from the humin fraction values. Two Histosol profiles collected under forest vegetation on a hillside presented very different morphologies and chronologies, possibly related to colluvium effect, indicated by the deposition of originally older material. The results for a Histosol profile under grassland indicates that C3 plants were the dominant vegetation over most of the last 8000 years at the most distant location while a Cambisol profile under transitional vegetation shows variations, with C3 plants at ca. 2 kyr BP, switching to C4 before ca. 700 yr BP, suggesting anthropic influence.