Ecosystem carbon pools, fluxes, and balances within mature tallgrass prairie restorations

Tallgrass prairie restorations can quickly accrue organic C in soil and biomass, but the rate of C accumulation diminishes through time and is highly variable among more mature prairies. Long-term soil organic carbon (SOC) accumulation in prairies has been linked to edaphic factors such as soil texture, soil moisture, and SOC content, but it is unclear how these factors affect the ecosystem processes that are responsible for observed differences in C accumulation rates in older prairies. We measured belowground plant and SOC pools and fluxes within 27-36-year-old restored tallgrass prairies in order to quantify total C storage, determine the net ecosystem production of C (NEP-C), and explore which edaphic factors influence the ecosystem processes responsible for divergent NEP-C. We found that 11% of organic C was stored in biomass, and we estimate that one-third of post-restoration C sequestration has occurred in biomass, thereby highlighting biomass as a large but often overlooked C pool. Belowground biomass and soil C pools were notably smaller than those reported for remnant prairie, suggesting that future belowground C accumulation could still occur. During this study, the prairies appeared to be a net source of C, although the range of NEP-C values encompassed zero. Sand content positively affected NEP-C via increased belowground biomass production-C inputs, and SOC negatively affected NEP-C due to increased soil respiration C outputs. However, soil moisture had a smaller negative effect on soil respiration, indicating that both SOC and soil moisture play important roles in determining prairie C balance.