Phytoliths as indicators of pedogenesis and paleoenvironmental changes in Spodosols of the state of Rio de Janeiro, Brazil.

This study aims to contribute toward a better understanding of the current biodiversity patterns existing in the Atlantic Forest of the state of Rio de Janeiro from a paleo-ecological approach. Three soil profiles, each formed from distinct source materials under varied climate and vegetation conditions were selected from the coastal regions of Rio de Janeiro, Brazil. Soil horizon samples for chemical and physical characterization were collected from 10 cm-interval depths, and the total organic carbon was determined in addition to performing isotype and phytolithic analyses. The phytolithic analysis associated with the isotopic techniques (δ13C) permitted the characterization of three stages of paleo-environmental evolution for the studied soils, presenting valid trends that indicate small variations within the phytosociological structure of the vegetation along a Spodosols line in the studied areas. These stages indicated that the phytolithic assemblage was formed from a vegetation profile containing more trees, adapted to conditions colder than the existing vegetation, although no environmental changes were detected using the isotopic data. The milder temperature conditions may have favored the pedogenetic processes of the spodic B horizon formation as well as the maintenance of the organic matter contained in the soil. This study serves as the first draft for the paleo-environmental association among the regions where the analyzed profiles are found.