U.S. Department of Energy Office of Biological and Environmental Research

PI-Submitted Research Highlights for
Terrestrial Ecosystem Science Program

An observational constraint on stomatal function in forests: evaluating coupled carbon and water vapor exchange with carbon isotopes in the Community Land Model (CLM4.5)

David R. Bowling
University of Utah

Highlight

The model simulation of δ13C of A) bulk needle tissue, B) bulk roots and C) bulk soil carbon. The different model simulations are solid or dashed colored lines, whereas the observations are the single points with uncertainty bars.  The solid lines and dashed lines in the middle panel represent living roots and structural roots respectively.  This figure demonstrates that the model can reasonably simulate the observed concentration of stable carbon isotopes within biomass at a forested Rocky Mountain site.

19 September 2016
Stable carbon isotopes allow for the calibration and improvement of land surface models

The Science
We used continuous observations of stable carbon isotopes that are exchanged between the land and atmosphere to better understand how a forest in the Rocky Mountains of Colorado responded to stressful growing conditions.

The Impact
Stable carbon isotopes provide a useful and independent constraint upon stomatal conductance –an important ecosystem parameter that controls the carbon and energy balance at the land surface.  Isotopes can also help guide improvements in how nitrogen limitation is represented within the land model component of a climate model.

Summary
We use stable carbon isotopes of CO2 to improve the performance of a land surface model, a component within earth system climate models. We found that isotope observations can provide important information related to the exchange of carbon and water from vegetation driven by environmental stress from low atmospheric moisture and rate of carbon assimilation (photosynthetic rate).  This information provided by isotope observations can go beyond what has traditionally been provided by land surface exchange of carbon, heat and water measured from towers.   Unexpectedly, we also found that isotope observations provided guidance upon how nitrogen limitation should be represented within models.  It follows that isotopes have a unique potential to improve model performance and provide insight into land surface model development.

Contacts (BER PM)
Daniel Stover and Jared DeForest
SC-23.1
Daniel.Stover@science.doe.gov (301-903-0289) and Jared.DeForest@science.doe.gov (301-903-1678)
(PI Contact)
David R. Bowling
University of Utah, Department of Biology
David.Bowling@utah.edu (801-581-2130)

Funding
DOE BER TES

Publications
Raczka, B., Duarte, H. F., Koven, C. D., Ricciuto, D., Thornton, P. E., Lin, J. C., and Bowling, D. R.: An observational constraint on stomatal function in forests: evaluating coupled carbon and water vapor exchange with carbon isotopes in the Community Land Model (CLM4.5), Biogeosciences, 13, 5183-5204, doi:10.5194/bg-13-5183-2016, 2016.

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