Changes in carbon and nitrogen cycling across a twenty six-year chronosequence of prairie restoration

The main objectives of this study were (1) to assess the time course of changes in key ecosystem properties and processes in a tallgrass prairie restoration project, and (2) to identify the mechanisms that could broadly explain these changes. These objectives were addressed using a 26-year chronosequence of tallgrass prairie restoration plots that provides a unique setting because of its high degree of temporal resolution. This study also examined the extent of spatial and temporal heterogeneity of soil resources and how these patterns changed with restoration age.; Vegetation composition, species richness, and productivity all showed dramatic changes with restoration age. By eight years following restoration seeding, the restoration plots were dominated by C₄ prairie grasses and had diverged significantly from an old-field condition, but diversity remained much lower than at the native prairie. Total C and soil moisture increased with increasing restoration age, while bulk density and soil temperature decreased. In contrast, there was little change in inorganic N, net N mineralization, or net nitrification rates across the chronosequence. Soil inorganic N concentrations and net N mineralization rates were positively correlated with soil moisture, however.; A study of mound-building ants found that the total basal area of ant mounds increased significantly with increasing restoration age. At the 8-year old site, mounds were enriched significantly in total N, dissolved organic N, nitrate, and ammonium; mounds also had significantly higher soil moisture compared to surrounding soil. These differences between soil on- and off-mounds disappeared by 26 years. Results from a geostatistical analysis of soil C and N indicated that there was a decrease in the magnitude of spatial heterogeneity at a macro-scale with increasing restoration age, suggesting that the increasing dominance of C₄ grasses across the chronosequence is homogenizing SOM content at the field scale.; The experience of 26 years of restoration demonstrates that changes in vegetation imposed by the restoration treatments have significant direct and indirect effects on C and N cycling. The challenge for future restoration projects remains how to take advantage of these changing functional properties in the ongoing quest to increase and maintain species diversity at restoration sites.