S. E. Melzer1, E.F. Kelly1, C.M. Yonker1, A.K. Knapp1, O.A. Chadwick2, Melinda D. Smith3, Richard W.S. Fynn4, and Kevin Kirkman4. (1) Colorado State University, (2) University of California, (3) Yale University, (4) University of KwaZulu-Natal
The contribution of biogenic silica (BSi) to ecosystem Si pools as well as the influence of BSi on weathering rates in terrestrial systems must be understood in order to further quantify the global biogeochemistry of Si. Recent research suggests that BSi production and storage may be most important in grass-dominated ecosystems relative to other terrestrial biomes. In this study, we identify and quantify the primary ecological and pedological drivers of the terrestrial Si cycle in grass dominated ecosystems. We sampled sites within the temperate grasslands of North America and in sub-tropical savannas and grasslands of South Africa to fill critical knowledge gaps and to further improve our assessment of the range and variability of BSi in grasslands globally. Although these sites share many similarities, they also have unique ecological, pedological and geological attributes that make them valuable for assessing potential controls on BSi. Our objectives were as follows: 1) to quantify the production, storage, and output of BSi within and among grass dominated ecosystems, and 2) to identify key controls on the size of the BSi pools by sampling sites that differ in (A) precipitation amount, (B) parent material, (C) age, and (D) fire regime. Our results show that, in the younger temperate grasslands, BSi derived from plants significantly increased (α=0.05) as a function of mean annual precipitation. In contrast, in the older, sub-tropical systems of South Africa, BSi decreased (α=0.05) as a function of an increasing mean annual precipitation. A comparative assessment of the importance of additional pedological and ecological regulators of BSi storage and mobilization in these grass-dominated ecosystems will be presented.
