How Deep Should We Go to Understand Roots at the Top of the World?

The Science

Rooting depth distribution describes the spatial extent of plant control over biogeochemical cycling and thus carbon feedbacks. Because soils in northern biomes store more organic carbon than equatorial biomes, small changes in roots’ depth distribution in these biomes have gross effects on carbon emissions. Current regional scale modeling efforts infer rooting depth distribution from aboveground features, which Blume-Werry et al. (2023) found too coarse to capture variability in modeled emissions from measured variation in rooting depth distribution. This commentary builds upon the work of Blume-Werry et al., proposing a root-focused plant functional type (PFT) framework to better capture rooting depth distribution.

The Impact

Blume-Werry et al. found that naturally standing variation in rooting depth distribution in the Arctic greatly affected modeled carbon emissions (cumulative 7.2 to 17.6 Pg C by 2100) via root priming of decomposition. This effect was not explainable with relationships derived from aboveground vegetation mapping units, complicating modelers’ ability to make inferences of belowground dynamics from more easily measured aboveground vegetative cover. Blume-Werry et al. propose a “root profile type” classification for future work, which this commentary expounds upon while proposing a coarse-scale and root-focused PFT framework.

Summary

Modeled carbon emissions from Arctic soils can vary drastically depending on how deeply Arctic plants grow the bulk of their roots (Blume-Werry et al. 2023). However, this variation was greater within vegetation mapping units than between, which the authors demonstrated through comparisons of rooting depth distributions estimating for each mapping unit and post hoc clustering of rooting depth distributions into shallow, intermediate, and deep “root profile types.”

In this commentary, researchers expand upon the root profile type concept, outlining a PFT framework predominantly grounded in plant belowground features thought to be relevant in Arctic and boreal ecosystems with carbon-rich soils. This PFT framework is likely suitable to such a task as it is more finely resolved to the scale at which rooting depth distribution varies meaningfully more between groups than within (i.e., mapping units) but not so finely resolved as to become intractable (i.e., species). Additionally, the PFT approach takes the belowground-focused perspective of Blume-Werry et al. but converts their analytical approach from an after-the-fact clustering to a predictive framework.

Principal Investigator

Sören Weber
Oak Ridge National Laboratory
[email protected]

Program Manager

Daniel Stover
U.S. Department of Energy, Biological and Environmental Research (SC-33)
Environmental System Science
[email protected]

Funding

This work was made possible by both the Spruce and Peatland Responses Under Changing Environments (SPRUCE) experiment and Next-Generation Ecosystem Experiments (NGEE) Arctic project, which are each funded and supported by the Biological and Environmental Research program in the U.S. Department of Energy’s (DOE) Office of Science. Oak Ridge National Laboratory is managed by UT-Battelle, LLC, for the U.S. DOE under contract DE-AC05-00OR22725.

Related Links

• Blume-Werry et al. (2023)

References