A path forward for the improved representation of fine roots in terrestrial biosphere models

Background/Question/Methods

Ephemeral roots with a narrow diameter (“fine” roots) are responsible for most plant nutrient and water uptake, contribute organic carbon throughout the soil profile in the form of labile root exudates and decomposing root material, and strongly influence ecosystem CO₂ and CH₄fluxes through respiration, rhizosphere oxygenation, and passive transport. Global terrestrial biosphere models are used to represent ecosystem processes and functions, and their feedbacks to the atmosphere, across the diverse biomes of Earth. Fine roots are poorly represented in large-scale models, meaning a key component of ecosystem dynamics is missing. Reasons for the overly-simplistic representation of roots include poor empirical understanding (and therefore representation) of important processes, limited communication among empiricists and modelers, and lack of data from ecosystems spanning the globe. Our objective is to develop a path forward to improve the representation of fine roots in terrestrial biosphere models in order to better project responses of terrestrial ecosystems to global change.

Results/Conclusions

Ecologists are increasingly asked to distill their measurements in a way that can inform and improve mechanistic model representation. A path forward to improve the representation of fine roots in terrestrial biosphere models requires root and rhizosphere ecologists to: (1) Proactively communicate important relationships among belowground processes to modelers through workshops, collaboration, and lunch dates. (2) Improve their access to, and understanding of, the treatment of fine roots in terrestrial biosphere models. This can be facilitated by novel methods to modularize tens of thousands of lines of model code to allow portions of large-scale models to be run on a personal computer rather than a super computer. (3) Develop mechanistic relationships among root function, changing environmental conditions, and more easily-measured plant traits (above- and belowground) in order to simplify model representation of complex processes. (4) Populate a global root database to provide an easily-accessible source of data for models and modelers, and to facilitate the parameterization of plant functional types at a global scale. (5) Pursue technological advancements, including links among root function and high-resolution soil microclimate conditions, as well as new experiments, including root growth responses to environmental change, to improve our understanding and modeling of roots and the rhizosphere.