Stabilized Soil Organic Carbon Pools in Subsoils under Forest Are Potential Sinks for Atmospheric CO2

Abstract

Abstract The soil organic carbon (SOC) pool stored in subsoil horizons in forests plays an important role in the global carbon cycle. Strategies are needed to increase the subsoil SOC pool in forests because the turnover time of SOC increases with increase in soil depth as subsoil SOC is chemically and physically stabilized. We compared the total SOC and total nitrogen (TN) pools, chemically and physically separated SOC fractions, and C and N pools in fine roots in a soil pedon in an oak-hickory forest type consisting of white oak (Quercus alba L.) and red oak (Quercus rubra L.) with yellow-poplar (Liriodendron tulipifera L.) at the North Appalachian Experimental Watershed near Coshocton, Ohio, USA. The SOC pool was the highest in the A horizon (47.4 Mg ha−1) and smaller in the Bt1 (6.9 Mg ha−1) and Bt2 (6.7 Mg ha−1) horizons. The SOC and TN concentrations sharply decreased with depth. Fine root C and N pools were much larger in the A horizon (0.71 and 0.025 Mg ha−1) than in underlying horizons. Although only 22% of the SOC pool was stored below the A horizon, 58% of the chemically stabilized and 31% of the physically stabilized SOC fractions pool occurred in the subsoil horizons. Thus, studies are needed to test whether forest management can increase the stabilized SOC pool in subsoil horizons to mitigate the human-induced climate change.