In recent decades, prairie restoration projects have become commonplace in many areas that were once primarily agricultural fields. Therefore, it is important to understand the ecological implications of prairie restoration. We are particularly interested in how biogeochemical processes change as a restored field ages and becomes an established prairie ecosystem. In addition, as restored prairies are often maintained through prescribed burns, we are interested in how fire may affect biogeochemical processes of restored fields. To answer these questions, we studied 6 fields, including a chronosequence of 5 restored plots on the campus of St. Olaf College in Northfield, Minnesota, and one agricultural field. Plots ranged from 3 to 18 years since restoration, with a cultivated soybean field serving as age 0. Time since burn for plots ranged from 0.5 to 3.5 years. In each restored plot we measured soil CO₂ flux, above and belowground biomass, nitrification and N mineralization, microbial C:N, percent moisture, percent C and percent N in the soil and total organic matter.

Results/Conclusions:

Total organic matter, percent moisture and percent C all decreased with time since restoration, while soil CO₂ flux and total microbial C:N increased with time since restoration. Our data strongly suggest nitrogen limitation of biological processes in all restored prairies. C:N ratios of microbes increased as a function of time since restoration, and plant C:N increased with time since previous burn, likely due to a decline in relative N availability. Percent N, nitrification and mineralization did not show significant temporal patterns, but did have significant spatial variation. Our data suggest that time since burn has a strong influence on aboveground variables while age since restoration influences belowground variables.