Caracterização de fitólitos de plantas e assembleias modernas de solo da caatinga como referência para reconstituições paleoambientais

Abstract

The Caatinga is the fourth Brazilian phytogeographical domain in number of angiosperm species, composed of a mosaic of dry forests and shrub vegetation, with enclaves of humid montane forests and savanna. Despite this, it is the second Brazilian biome in terms of least protected areas in its domain and has few paleoenvironmental studies. In order to contribute to the discussion on the evolution of this biome during the Quaternary, phytoliths were chosen as indicators. As this is a pioneering study for this type of proxy in the region, it was first necessary to investigate whether the plants of the Caatinga are producers of phytoliths and if they are preserved in the soils. Samples of 33 plants from 16 families and 5 superficial soil samples (Modern Assemblages) were collected in the Northern Sertaneja Depression (MA1 - Caatinga Open Shrubland, MA2 - Medium Caatinga Forest, MA3 - High Caatinga Forest, MA4 - Riparian Forest and MA5 - Dense Caatinga Shrubland) to be used as reference for future work with fossil assemblies. We found that the Caatinga plants are good producers of phytoliths, predominantly tracheids, polyhedral, globular granulate and trichomes. The analyses of the 5 modern assemblages indicated a good degree of phytolith preservation, varying in type and quantity according to the overlying vegetation and granulometry of the soil. The group with the highest number of classifiable phytoliths was MA3, while MA1 presented the lowest percentage. The largest stocks of phytoliths were found in MA 3, 2 and 5, and the lowest in MA 1 and 4. The predominant phytolyth morphotypes were globular granular echinate and elongate, which is expected in this type of vegetation. The phytolyth indexes D/P (0.6 to 15), Bi (50 to 78%), Iph (53 to 87%) and Pa/P (0.1 to 8.9) are compatible with the type of vegetation analyzed. Phytoliths have been shown to be promising tools for better knowledge of the region's vegetation, as well as for paleoenvironmental studies in the biome.