Submitted to: Ecological Society of America Abstracts
Publication Type: Abstract only
Publication Acceptance Date: 7/22/2011
Publication Date: 8/7/2011
Citation: Hockaday, W.C., Gallagher, M.E., Masiello, C.A., Polley, H.W., Baldock, J.A., Pyle, L.A. 2011. Biochemical inventory as a tool to assay ecosystem carbon dynamics. In: Proceedings of the Ecological Society of America, August 7-12, 2011, Austin, Texas. OOS 11-8. Interpretive Summary:
Technical Abstract: Global soil carbon (C) stocks (2 x 1018 g C) are large enough that a minor change in soil C dynamics would constitute a major climate feedback. The responses of soil C stocks to experimental manipulations of atmospheric carbon dioxide concentration (CO2) and temperature vary widely in direction and magnitude across different ecosystems. The reasons for these differences are not well understood. Biochemical inventories in biomass and soil C pools give a new perspective on ecosystem C dynamics. A comparison of biochemical stocks in the soil to the fluxes from roots and shoots (e.g. kg carbohydrate/m2·yr) provide insight to C cycling mechanisms. We performed biochemical inventories for native grassland ecosystems on 3 different soil types (Mollisol, Alfisol, and Vertisol) and under varying (CO2) at the USDA CO2 Tunnel Experiment (Temple, TX). We used 13C nuclear magnetic resonance to study the chemical structure of plant tissues and soil organic matter and applied a molecular mixing model (Baldock et al., 2004) to estimate biochemical stocks. Biochemical fluxes to the soil surface were affected by soil order, through differences in net primary productivity (NPP) and plant species distribution within the community. Of the 3 soil orders, the Mollisol, a clay-rich alkaline soil, had the lowest NPP (278 g/m2·yr) and the lowest carbohydrate fluxes to the soil surface (205 g/m2·yr). Despite the lower inputs, the Mollisol had the highest carbohydrate stock in the soil (34% of the soil C). This suggests that the mineralogy and/or structure of the Mollisols preserve labile organic matter more efficiently than the Alfisol and Vertisol. Conversely, the Vertisol grassland ecosystem had the highest lignin production (91 g/m2-yr) and the lowest soil lignin stocks (660 g lignin/m2·yr), perhaps indicating higher fungal activity than in the Mollisol and Alfisol. The Alfisol showed the largest response to (CO2). Ecosystem carbohydrate production increased from 92 g carbohydrate/m2·yr), at 292 ppm (CO2) to 417 g/m2·yr) at 476 ppm (CO2). Despite this, soil carbohydrate stocks declined from 1300 g/m2 to 600 g/m2, perhaps suggesting a (CO2)-induced priming of microbial activity in sandy, acidic soils. Here we will further explore the utility of biochemical inventories as a tool for understanding ecosystem C dynamics.