Soil weathering: The puppet master of carbon cycling?
Soils are important for carbon (C) storage and thus for possible mitigation of atmospheric CO₂ concentrations. In a recently published Nature Geoscience article, scientists took a closer look at the drivers of C storage in soils. The study along a 3-million-year old terrace sequence in the Californian central valley shows how soil weathering controls and influences crucial parts of terrestrial C cycling.
Augsburg/SD/KPP – Quantifying soil C dynamics is crucial in the context of global change because soils play an important role in the exchange of CO₂ between land and atmosphere. Whether C is stored in soils or released back to the atmosphere is usually related to climatic factors and land management, as they control plant growth and the activity of soil microorganisms. Geochemistry, however, can be seen as the stage in which soils develop and C is cycled.
An international team of researchers led by Sebastian Doetterl from Augsburg University, Germany, and Asmeret A. Berhe from the University of California, Merced, USA shows why it is important to understand long-term mineral weathering when assessing short-term responses of soil C dynamics.
“Our models fail to accurately represent the influence that soil weathering (it is, changes in geochemistry of soils over time) can have on present and future soil carbon dynamics”, Doetterl says. The international team of researchers showed the importance of weathering processes lasting from only a couple to millions of years and how this affects plant growth, microbial communities and stabilization of soil C over time.
The scientists worked along a soil chronosequence originating from the same geologic material and developed under similar climate and vegetation cover. The youngest soils along this sequence are only a few years old, whereas the oldest, and highly weathered soils are several million years old. “This difference in development stage of soil allowed us to investigate all kinds of changes that occur over time to the C cycle. For example, changes in vegetation types due to differing availability of nutrients, changes in microbial communities and their strategies to assess these nutrients, the capacity of minerals to stabilize C in soils and the effect that warming might have on biological processes”, Berhe adds. The researchers demonstrate that biogeochemical alteration of the soil matrix (and not short-term warming) controls the composition of microbial communities and strategies to metabolize nutrients. More specifically, weathering first increases and then reduces nutrient availability and retention, as well as the potential of soils to stabilize C.
So how does this knowledge help to improve predictions of the future C cycle?
“The great thing about our findings is that they show biological processes that act on short time scales are closely tied to the long term changes in soils that come with weathering”, Doetterl continues. “We hope that this understanding will instigate a better integration of weathering mechanisms into models by ecologists and biogeochemists to predict C at the global scale. If biology, that drives the C cycle, is controlled by geochemical changes in soils, we can use much simpler approaches and larger datasets of soil properties and underlying geology to create better predictions of future developments of the C cycle”, he concludes.
Doetterl S., Berhe A.A., Arnold C., Bodé S., Fiener P., Finke P., Fuchslueger L., Griepentrog M., Harden J.W., Nadeu E., Schnecker J., Six J., Trumbore S., Van Oost K., Vogel C., Boeckx P. 2018. Links among warming, carbon and microbial dynamics mediated by soil mineral weathering. Nature Geoscience, https://doi.org/10.1038/s41561-018-0168-7.
Dr. Sebastian Dötterl
University of Augsburg