|Johnson, H - COLLABORATOR|
|Romanek, C - UNIVERSITY OF GEORGIA|
Submitted to: American Geophysical Union
Publication Type: Abstract Only
Publication Acceptance Date: November 7, 2008
Publication Date: December 23, 2008
Citation: Jin, V.L., Fay, P.A., Polley, H.W., Johnson, H.B., Romanek, C.S. 2008. Changes in pedogenic carbonate accumulation under altered atmospheric CO2 in a mesic calcareous grassland. In: Proceedings of the EOS Trans. American Geophysical Union. December 15-19, 2008, San Francisco, CA. Paper No. B13A-0437. Technical Abstract: Numerous studies have examined the effect of elevated atmospheric CO2 on organic carbon (C) cycling, but less is known about the impacts of changing CO2 on inorganic C processes. Pedogenic carbonates are derived from C released during the decomposition of soil organic matter. Thus, increases in soil respiration resulting from the effects of increasing atmospheric CO2 on ecosystem productivity could impact the sequestration of C in inorganic C pools via pedogenic processes. We examined potential changes in pedogenic carbonate accumulation at different atmospheric CO2 concentrations in an intact ecosystem of mesic calcareous grassland. Plots were exposed to a CO2 gradient ranging from pre-Industrial (200 µL L-1 to mid-21st century concentrations (550 µL L-1) during the growing seasons from 1997 to 2000. Pre- and post-CO2-treated mineral soils were sampled at four depth increments from the soil surface to 53 cm depth in plots exposed to high, ambient, and low CO2 (550, 360, and 200 µL L-1, respectively). Pedogenic carbonate accumulations were quantified with an isotopic mixing model using d13C values of bulk, pedogenic, and parent carbonate in soils. Isotopic values of the pedogenic carbonate end-member were estimated using the diffusion model of Cerling (1984), and the parent carbonate value was measured from a weakly developed modern floodplain soil at a nearby site (Nordt et al. 1998). For all post-CO2 treatment soils, the amount of pedogenic carbonates was greatest in 8-37 cm subsoil, and was positively correlated to soil organic matter C (SOM-C). Compared to pre-CO2 treatment soils, SOM-C concentrations did not change in surface soils (0-8 cm) exposed to low and ambient CO2, but increased 31% to 44% in subsurface soils (8-53 cm). Soils exposed to high CO2 increased in SOM-C in both surface and surface soils by 40% to 280% of pre-treatment soils, respectively. Further, the d13C of bulk carbonate decreased as SOM-C increased across all soils, reflecting the isotopic signature of fossil CO2 used to augment atmospheric CO2 concentrations over four growing seasons. Our results indicate that increases in soil organic C pools are affecting the formation of pedogenic carbonates in this calcareous grassland, with potential short- and long-term effects of altered atmospheric CO2 on soil C sequestration.