Granulometry of mineral soils affecting pollen records and paleoenvironmental reconstitution in South America Grasslands

Abstract

Mineral soils are generally considered unsuitable for pollen analysis because of poor pollen quality, low spore preservation, and disturbed stratigraphy. Our study aimed to determine the influence of particle size composition in the pollen record and contribute to reconstituting the paleoenvironmental history during the late Holocene in the Brazilian Pampa biome. Palynological, soil particle size, and radiocarbon dating (¹⁴C) analyses were performed on fifteen mineral soil samples of a Leptic Luvisol, collected in a grassland-forest ecotone area in the Brazilian Pampa biome, in southern Brazil. In the palynological analysis we identified 36 taxa from grassland, 25 from forest, and 9 non-pollen palynomorphs (NPPs). Five paleoecological zones were identified, and ¹⁴C indicated the age of 2630 ± 25 cal yr B.P. at 70 cm depth of soil. The highest values of pollen concentration occurred in the clay loam texture horizon, between 25 and 45 cm, with values of 396.30 cm³ at 30 cm depth Pollen concentration was lower in sandier soil horizons and higher in clay loam horizon, with a strong inverse relationship with coarse sand (r = −0.78) and positive with silt (r = 0.61) and clay (r = 0.52). These relationships show soil particle size is a fundamental property in pollen preservation, and should be used as a determinant factor when choosing soil type in palynology studies. Our study subsidizes the understanding of the biome flora, which is important for species richness and autochthony, and the results on floristic biodiversity may contribute to flora conservation and recovery of degraded areas in grasslands biome.