Phytoliths from soil surfaces and water reservoirs of the Brazilian semi-arid Caatinga

Abstract

Understanding processes that explain phytolith assemblages and their concentration in the soil and sediments is essential to interpret long-term ecological changes. The present study shows modern phytolith assemblages and their relationship with the vegetation cover in the Caatinga biome, state of Cear ́a, northeastern Brazil. We collected recent samples from soil surfaces, in 2015, in three different vegetation covers (open shrubby Caatinga, dense shrubby Caatinga, and Caatinga forest vegetation) and from two cores with recently deposited sediments, in Massapˆe (74 cm depth, 55 years old) and Varjota (50 cm depth, 58 years old). After phytolith extraction, we studied twelve samples from soils and thirteen samples from cores. The counting revealed 26 different phytolith types with some differences in the concentration of silica bodies in different vegetation covers. Phytoliths were well preserved and could be related to the presence of plants, such as Poaceae (subfamily Panicoideae and Chloridoideae), Arecaceae and Cyperaceae. In the two cores, the most common type was globular echinate and could be associated with the presence of palms in the riparian forest and open landscapes in the surroundings. In soil surfaces samples, the saddle was the most frequent type. We found a high concentration of globular granulate around Aiuaba Ecological Station, which harbors a preserved Caatinga area. Finally, we observed a good match between vegetation cover and the phytolith assemblages collected in soils and reservoirs.