The paleoenvironmental significance of fungal palynomorphs in a Quaternary peat from the Middle Paraíba do Sul River Valley, SP, Brazil

Abstract

This study deals with spores, conidia and hyphae of fungi present in a peatbog core from the Eugenio de Melo district, middle Paraíba do Sul river valley in the State of São Paulo, Brazil. Dated between 11,240 to 300 cal. years BP, the core comprises parts of two sedimentary cycles separated by a hiatus of about 7,000 years. Palynomorphs were extracted following standard procedures with the dissolution of mineral components and elimination of humid acids, followed by acetolysis. A total of 210 fungal palynomorphs were identified based on comparison with fossil and modern genera and species with the aim of determining their paleocological significance; diagrams were prepared of 40 palynomorphs selected as representative of the diversity of the assemblage which allowed three intervals to be estalished: Interval I between 360 and 190 cm depths with ages between 11,240 cal. yr BP and 8,930 years BP (interpolated age); Interval II between 191 and 110 cm depths and > 718 and 550 years BP (interpolated) in age; and interval III between 110 and 0 cm depths dated between 550 years BP (interpolated) and the present.The majority of the taxa found in this study are saprophytes, followed by leaf parasites as well as pathogens and fecal decomposers. The fungal spore assemblages along the sediment profile indicate growth and preservation within a reducing environment containing abundant decaying organic matter. Some mycorrhizal spores are associated with Cyperaceae/Poaceae in wet environments and/or with Poaceae in waterlogged conditions, which is indicative of open vegetation in both cases. The occurrence of Ascodesmisites malayensis, a saprophyte on Cyperaceae leaves, in sediments dated from 11,240 cal. years BP and 10,800 years BP (interpolated age) confirms a soaked substrate or highest levels of water. Anatolinites, a pathogenic genus thriving on leaves of living plants, occurs at the beginning of interval II, after a hiatus of about 7,000 years BP, when the area was covered by forests.Plant parasites of woody substrates, such as Diporicellaesporites cf. D. liaoningensis and Diporicellaesporites sp. 9, indicate prevailing arboreal vegetation during the first cycle of organic matter deposition. The abundance of Monoporisporites sp. 6, a fecal decomposer, which has been related to the presence of herbivorous animals within the last 300 years, is likely related to anthropogenic activities in the modern peatbogs.