Rising atmospheric CO2 concentrations have increased interest in the potential for forest ecosystems and soils to act as carbon (C) sinks. While soil organic C contents often vary with tree species identity, little is known about if, and how, tree species influence the stability of C in soil. Information on this stability is crucial to predict the vulnerability of C in forest soils to disturbances, such as shifts in species composition following climate change. Gerrit Angst from the SoWa Research infrastructure and the Institute of Soil Biology of the Czech Academy of Sciences and his American, German, and Polish colleagues investigated relationships between soil organic matter stability in mineral soils and various ecological factors. The work was published in the prestigious journal Global Change Biology.
The authors show that tree species regulate soil C stability via the composition of their tissues, especially roots. Stability of soil organic matter appeared to be greater beneath species with higher concentrations of nitrogen and lower amounts of recalcitrant compounds in their roots, while soil organic matter stability appeared to be lower beneath species with higher tissue calcium contents. These differences in soil C stability, though, were independent of the amount of C under the respective tree species. Thus, when considering forest soils as C sinks, the stability of C stocks must be considered in addition to their size. Some C stability indices, though, were insensitive to tree species identity and traits, reflecting a limited effect of tree species on some soil organic matter pools (e.g., mineral-associated C) on decadal timescales. Strategies aiming to increase soil C stocks may thus focus on particulate C pools, which can readily be manipulated and are most sensitive to climate change.