How do tree species affect soil organic carbon stability in forests?

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 C stability and various ecological factors (including tree tissue chemistry, magnitude of organic matter inputs to the soil and their turnover, microbial community descriptors, and soil physicochemical properties) under eleven different tree species. The work has been published in the prestigious journal Global Change Biology and represents the first comprehensive investigation on how tree species and their traits affect mineral soil C stability.

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 (i.e. poorly degradable) compounds in their roots (such European larch or Scots pine), while soil organic matter stability appeared to be lower beneath species with higher tissue calcium contents (such as small-leaved lime or Norway maple).

Notably, the differences in soil C stability were independent of the total amount of soil C under the respective tree species. This indicates that, when evaluating forest soils as C sinks, not only the amount of C in soil but also the stability of these C stocks must be considered. For example, Scots pine stood out as a species with relatively stable organic C in mineral soils and comparably large C stocks. In contrast, though having large C stocks, soils under sycamore maple had a relatively low C stability.

The results also showed that not all portions of C in soil (so called C pools) were affected by tree species. For example, the more stable pool of C, which may persist in the soil for decades or even centuries, was unaffected by tree species and their traits. This was either because the effects of tree species on this pool may not be detected on short time scales or abiotic factors, such as soil mineralogy and texture, might overshadow the role of trees. Opposite to that, the more labile C pools, such as partly stabilized particulate C (coarse organic material that is most similar to the vegetation it derives from) was sensitive to variations in tree species traits and may thus offer the greatest potential for managing forests as C sinks.

For more details, please see the full publication:

Angst, G., Mueller, K.E., Eissenstat, D.M., Trumbore, S., Freeman, K.H., Hobbie, S.E., Chorover, J., Oleksyn, J., Reich, P.B., Mueller, C.W., 2019. Soil organic carbon stability in forests: distinct effects of tree species identity and traits. Global Change Biology. doi:10.1111/gcb.14548