Monday, November 13, 2006

Effects of Topography and Contributions of C3- and C4-Sourced Carbon to the Rate of Soil Carbon Accumulation in Restored Tallgrass Prairie.

Sarah L. O'Brien1, Julie D. Jastrow2, and Miquel A. Gonzalez-Meler1. (1) University of Illinois at Chicago, Chicago, IL 60607, (2) Argonne National Laboratory, Argonne, IL 60439

Soils of degraded landscapes that have undergone revitilization may provide sinks for increasing atmospheric [CO2], especially in tallgrass prairie where substantial belowground productivity and highly structured soil provide good conditions for soil organic matter (SOM) accumulation and stabilization.  For the last three decades, a chronosequence of restored prairies at the Fermi National Accelerator Laboratory near Batavia, IL has been accumulating soil C, but the mechanisms that control the accrual rate and potential C saturation of the system are unknown.  This study used a repeated measures approach rather than the chronosequence method to determine a rate of soil C accrual for each of four restored prairies and a field of Bromus inermis, a non-native C3 grass.  Stable isotope signatures of the soil carbon were used to determine accumulation rates for C3- and C4-sourced C.  After 15 to 30 years since planting, prairies located in topographically lower areas appeared to have a faster rate of C accumulation compared to topographically higher plots, while the brome field remained in equilibrium with respect to soil C.  In addition to physical protection, SOM stabilization may come from the seasonally flooded conditions in the low lying prairies which may create a microclimate that inhibits C mineralization.  The prairies that exhibited the fastest C gain had the highest increases in C4-C, which was not necessarily related to biomass of C4 plants.  The lower quality of organic matter from prairie plants, which include many C4 grasses, compared to C3 grasses like B. inermis, may lead to faster C accumulation.