Stable isotope ratios of soil carbonate and soil organic matter as indicators of forest invasion of prairie near Ames, Iowa.

Stable isotope ratios of pedogenic carbonate and organic matter were measured in a prairie-transition-forest soil biosequence near Ames, Iowa to determine the vegetation succession. The modern vegetation is dominated by non-native C3 plants which have been introduced by agricultural practices. The δ13C values of soil organic matter from the prairie and forest endmembers indicate C4 and C3 dominated ecosystems, respectively, during the accumulation of soil organic matter. Pedogenic carbonate from all soils, including rare pedogenic carbonate from the forested soil, has an average δ13C of-2.0‰, indicating that the carbonate formed under a C4 vegetation. These results indicate that the ecosystem was a C4-dominated prairie and therefore suggest a recent arrival of forests and other C3 plants in the area. This study also implies that the primary features of the transitional Lester soil series, which has soil properties intermediate between Alfisols and Molisolls, formed under prairie conditions and were overprinted by an invading forest.