COLLABORATIVE RESEARCH: Ecological Controls on Biogenic Silica in Grasslands - The Role of Long-term Fire and Grazing History on Two Continents

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This research will investigate the quantities and chemistry of biogenic Si (plant-derived silica) along climatic and geologic gradients in grassland ecosystems of the central Great Plains of North America and the savannas of the South Africa. Factors that affect the production, storage, and chemical behavior of biogenic Si in geographically diverse grassland ecosystems will be identified. Furthermore, the influence of grazing and fire in grasslands on biogenic Si will be assessed. The terrestrial production, movement and cycling of silica is closely linked to the global carbon cycle. In the oceans, certain minute marine algae (diatoms) are a major control on the distribution of silica and also play a major role in controlling atmospheric CO2 concentration due to their photosynthetic activity. The importance of biological controls on silica cycling in the terrestrial environment is much less well known, but likely results from the formation and storage of biogenic silica in plants and soils, particularly in grasslands. Recent estimates suggest that the global uptake of biogenic silica by terrestrial vegetation rivals quantities stored in the biologically active portions of the ocean systems. More importantly, the largest reservoir of biogenic Si in terrestrial systems resides not in living biomass but in soils and, in particular, grassland soils. Biogenic silica accumulates belowground upon death and decomposition of plant materials. This large reservoir of biogenic Si in grasslands may be greatly influenced by global change factors, with unknown consequences for global biogeochemical cycles.