Silicophytoliths in representative soils of the southeast pampean plains, Argentina

Abstract

The soil is an open, complex, multi-structural and multi-functional system that requires many disciplines and scientific approaches to study it. Few studies use biotic activity as a tool to determine pedogenesis. In this sense, silicophytoliths, biomineralizations produced by plants, are considered good current and fossil pedogenetic and environmental indicators. In this chapter a summary of the results gathered from the silicophytolith studies in characteristic soils (Argiudolls, Hapludolls, Alfisolls and Entisolls) of the southeast Pampean Plains is discussed. Geopedological units, developed in four typical geomorphological units of the Pampean plains, were defined based on integrated topographic, geomorphologic and pedologic studies. In each unit, modal soil profiles were morphologically described according to routine techniques. Soil samples were subjected to different methodologies so as to eliminate carbonates, organic matter and clays. The silicophytolith content was determined as a percentage of the mineralogical components. The silicophytolith morphologies were described under light microscope according to reference bibliography. In general, a direct relationship was found between the intensity of the pedogenetical process, the content of organic matter and the content or percentage of silicophytoliths. The greater silicophytolith contents were found in the molic horizons in comparison with the endopedions and parental material. In the coastal environment, there is no correlation between pedogenetical evolution and silicophytolith content and the values obtained are similar to the molic horizons of pedogenetically well-evolved soils. The silicophytolith assemblages described in the different types of soils mainly represent the local vegetation, dominated by grasses. However, the pool of silicophytoliths includes some morphologies produced by regional or extra-local species which were transported by different agents or processes. In all soils in all the geopedological units studied, the dissolution or fragmentation process of silicophytoliths is particularly important, with a key role in the biogeochemical cycle of Si and in the formation of amorphous silica enriched matrices. Silicophytolith studies add complementary data and information to the results gathered by other proxies and these have proven to be a good pedological, paleoecological, paleoenvironmental and archeological indicator.