Differential soil organic carbon storage at forb- and grass-dominated plant communities, 33 years after tallgrass prairie restoration

Abstract

Dominance of C4 grasses has been proposed as a means of increasing soil organic carbon (SOC) sequestration in restored tallgrass prairies. However, this hypothesis has not been tested on long time scales and under realistic (e.g. N-limited) environmental conditions. We sampled a restoration in southern Illinois 33 years after establishment to determine the effects of varying plant communities on SOC sequestration in the top 50 cm of soil. SOC, total nitrogen (TN), and the stable isotopic composition of SOC (δ13C) were used to calculate SOC sequestration rates, N storage, and the relative contributions of C3 vs. C4 plant communities as a function of soil depth. While both a forb-dominated and a mixed forb-grass plant community showed positive sequestration rates (0.56 ± 0.13 and 0.27 ± 0.10 Mg C ha−1 yr−1, respectively), a C4 grass-dominated community showed SOC losses after 33 years of restoration (−0.31 ± 0.08 Mg C ha−1 yr−1). Soil δ13C values were significantly more negative for forb-dominated plant communities, increasing the confidence that plant communities were stable over time and an important contributor to differences in SOC stocks among transects. These results suggest that functional diversity may be necessary to sustain sequestration rates on the scale of decades, and that dominance of C4 grasses, favored by frequent burning, may lead to SOC losses over time.