Silica Biogeochemical Cycle in Temperate Ecosystems of the Pampean Plain, Argentina

OSTERRIETH, MARGARITA; BORRELLI, NATALIA; ALVAREZ, M. FERNANDA; FERNÁNDEZ HONAINE, MARIANA

JOURNAL OF SOUTH AMERICAN EARTH SCIENCES

PERGAMON-ELSEVIER SCIENCE LTD

Año: 2015 vol. 63 p. 172 - 179

0895-9811

Silicophytoliths were produced in the plant communities of the Pampean Plain during the Quaternary.The biogeochemistry of silicon is scarcely known in continental environments of Argentina. The aim ofthis work is to present a synthesis of: the plant production and the presence of silicophytoliths in soilswith grasses, and its relationship with silica content in soil solution, soil matrix and groundwaters intemperate ecosystems of the Pampean Plain, Argentina. We quantified the content of silicophytoliths inrepresentative grasses and soils of the area. Mineralochemical determinations of the soils' matrix weremade. The concentration of silica was determined in soil solution and groundwaters. The silicophytolithsassemblages in plants let to differenciate subfamilies within Poaceae. In soils, silicophytoliths represent40e5% of the total components, conforming a stock of 59e72 _ 103 kg/ha in A horizons. The concentrationof SiO2 in soil solution increases with depth (453e1243 mmol/L) in relation with plant communities,their nutritional requirements and root development. The average concentration of silica ingroundwaters is 840 umol/L. In the studied soils, inorganic minerals and volcanic shards show no featuresof weathering. About 10e40% of silicophytoliths were taxonomically unidentified because of theirweathering degrees. The matrix of the aggregates is made up by microaggregates composed of carbonand silicon. The weathering of silicophytoliths is a process that contributes to the formation of amorphoussilica-rich matrix of the aggregates. So, silicophytoliths could play an important role in the silicacycle being a sink and source of Si in soils and enriching soil solutions and groundwaters.