INVESTIGADORES
ALVAREZ maria fernanda
congresos y reuniones científicas
Título:
Amorphous silica biomineralizationsin plants and soils, and their role in the biogeochemistry on silicon in the southeast of the pampean plain, Argentina
Autor/es:
OSTERRIETH, M.; N. BORRELLI; M.F. ALVAREZ; M. FERNANDEZ HONAINE; J.L DEL RÍO; H. GÓMEZ COE AND M. MADELLA
Reunión:
Congreso; 8th International Meeting on Phytolith Research; 2011
Resumen:
Amorphous silica biomineralizations (silicophytoliths) are commonly produced in the plant communities that have dominated the Pampean Plains during the Cenozoic. The transfer of amorphous silica from these biotic systems to soils in these temperate and wet Pampean environments is considered as a condition for silica biogeochemical processes. The biogeochemistry of silicon, the second most abundant element in the world, is poorly known in continental environments and particularly in the Pampean Plain of Argentina. This study includes Molisols and Fluvisols (and their vegetation) from dry environments, ponds and groundwaters. Soils were analyzed at different scales (mega, meso, micro, and submicroscopic), with special emphasis in mineralochemical determinations. The presence of silicophytoliths and their weathering degree was assessed through routine methods in plants, soils, palaeosoils, and sediments. The concentration of silica was determined in the soil solution, the temporary ponds, the Los Padres wetland and its tributaries (Los Padres stream, inflow stream; and La Tapera stream, outflow stream), and in groundwaters. The results indicated that the amount of silica content ranged between 2% and 18% (dry weight) in the most common monocotyledons of the region, and between 1% and 4% in most dicotyledons. The content of silicophytoliths in epipedons of Molisols is high, with values of 59.6x103 - 103.5x103 Kg/ha. The concentration of SiO2, in soil solution and its distribution along the profile is variable and reflects present and past plant communities, the root development and the nutritional requiremenrs of the species. In plots planted with Acacia sp. and Eucalyptus sp., the concentration of SiO2, in the soil solution of the Mollisols decreases with depth (from 1106 to 406 µmol/L), whereas in plots with grass cover silica concentration increases with depth (from 421 to 777 µmol/L). Grasses are silica accumulators that have a shallow root system so the absorption from the soil solution is higher at the surface, and this could explain the lower silica content in epipedons with grass vegetation. The average concentration of silica in surface waters is 60 µmol/L. In Los Padres wetland, the silica content is 19.1 to 917 µmol/L, being higher in autumn and winter and decreasing in spring during the diatom boom. In the inflow stream, values increase (660-917.5 µmol/L) in relation to silica concentration in the soil solution and groundwater (where the average value is 840 µmol/L). The contribution of silicophytoliths by grass plant communities has been ongoing during all the Cenozoic and it has increased with agricultural and livestock exploitation during the last 150 years. These balances show that much of the silicon/amorphous silica re-circulates in the unsaturated zone, where it contributes to form an amorphous silica enriched matrix of aggregates, which increases and maintains the structural stability of soils. Part of the silicon/amorphous silica, however, moves to the saturated zone and associated waters.