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

本研究将沿着气候和地质梯度调查北美大平原中部和南非稀树草原草原生态系统中生物源硅（植物源二氧化硅）的数量和化学性质。在地理多样性的草地生态系统中，确定影响生物源硅生产、储存和化学行为的因素。在此基础上，分析了放牧和火灾对草地生物硅的影响。陆地二氧化硅的产生、移动和循环与全球碳循环密切相关。在海洋中，某些微小的海藻（硅藻）是二氧化硅分布的主要控制因素，由于它们的光合作用，在控制大气二氧化碳浓度方面也起着重要作用。生物控制对陆地环境中二氧化硅循环的重要性知之甚少，但可能是植物和土壤中，特别是草原中生物源二氧化硅的形成和储存的结果。最近的估计表明，全球陆地植被对生物硅的吸收与海洋系统中生物活性部分的储存量相当。更重要的是，陆地系统中最大的生物源硅库不存在于活的生物量中，而存在于土壤中，特别是草地土壤中。生物硅在地下随着植物材料的死亡和分解而积累。这一巨大的草原生物硅库可能受到全球变化因素的极大影响，对全球生物地球化学循环的影响尚不清楚。

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.