Carbon Cycling Across a Reconstructed Prairie Chronosequence.

Native prairie restorations placed on strategic locations can be an effective tool for increasing nitrogen and carbon within the soil. While there is much debate on the mode of action of this increase, chemical bonding with clay or physical protection through microaggregates is thought to stabilize carbon against loss. As this binding capability is theoretically finite due to limited surface area on clay particles, a decrease in the rate of carbon storage could occur after a number of years of prairie biomass inputs. However, binding of organic matter via cation bridging or iron oxides could also contribute to this stabilization. Nineteen reconstructed prairie plots with similar clay and silt content were selected from a chronosequence located at Neal Smith Wildlife Refuge in Prairie City, Iowa. Across 21 years, total soil carbon increased logarithmically (R2= 0.3513, p= 0.0075) with total carbon strongly related to the concentration of carbon on silt/clay outside of microaggregates (R2= 0.9055, p= <0.0001). Organic matter protected by microaggregates did not change significantly over 21 years of prairie reconstruction. Polyvalent cations also did not correlate to time or any soil fraction’s carbon concentration. However, non-crystalline iron oxide extractions were positively correlated with microaggregate silt/clay carbon concentration (R2= 0.3281, p= 0.0104) and its carbon to nitrogen ratio (R2= 0.3886, p= 0.0044). As iron oxides are considered to be relatively unimportant for organic matter stabilization in Mollisol soils high in 2:1 clays, future work will investigate the potential for iron oxides to accelerate microaggregate stabilization within reconstructed prairies.