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PI-Submitted Research Highlights for
Terrestrial Ecosystem Science Program

A Roadmap for Improving the Representation of Photosynthesis in Earth System Models

Alistair Rogers

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28 November 2016

Researchers identified key model development activities, data needs, and process knowledge improvements required to advance the representation of photosynthesis in next-generation climate models.

The Science  
A collaboration between modelers and plant physiologists compared the projected physiological responses of photosynthesis to key environmental drivers in seven terrestrial biosphere models (TBMs) that form the land components of major Earth system models. The study identified research activities needed to improve process representation of photosynthesis in TBMs.

The Impact
A widely held assumption is that the representation of photosynthesis in TBMs is settled science and that model uncertainty is driven largely by other processes downstream of carbon acquisition. This study demonstrates that model divergence in the physiological response of photosynthesis to key environmental drivers is high and likely a major source of model divergence. This finding is critical because the response of the terrestrial biosphere to global change is driven by these same physiological responses and their accurate representation should be an essential component of improved TBMs. The study lays out the steps needed to improve model representation of photosynthesis.

Summary
Accurate representation of photosynthesis in TBMs is essential for robust projections of global change. However, current representations vary markedly between TBMs, contributing uncertainty to projections of global carbon fluxes. In this study, researchers compared the representation of photosynthesis in seven TBMs by examining leaf and canopy-level responses of photosynthetic carbon dioxide (CO2) assimilation to key environmental variables: light, temperature, CO2 concentration, vapor pressure deficit, and soil water content. They identified research areas where limited process knowledge prevents inclusion of physiological phenomena in current TBMs and research areas where data are urgently needed for model parameterization or evaluation. The study provides a roadmap for new science needed to improve the representation of photosynthesis in the next generation of terrestrial biosphere and ESMs.

Contacts
BER Program Manager
Daniel Stover and Jared DeForest
SC-23.1
Daniel.Stover@science.doe.gov (301-903-0289)
Jared.DeForest@science.doe.gov (301-903-1678)

Principal Investigator
Alistair Rogers
Brookhaven National Laboratory
Upton, NY 11973-5000
arogers@bnl.gov

Funding
The New Phytologist Trust provided support of the 9th New Phytologist Workshop – Improving representation of photosynthesis in Earth System Models. AR and SPS were supported by the Next-Generation Ecosystem Experiments (NGEE)–Arctic and NGEE–Tropics projects that are supported by the Office of Biological and Environmental Research, within the U.S. Department of Energy (DOE) Office of Science, and through DOE Contract No. DE-SC00112704 to Brookhaven National Laboratory; DW acknowledges support from NSERC, CFI, and an Ontario ERA award. JSD received support from the National Science Foundation (DEB-0955771).

Publications
Rogers A., Medlyn B.E., and Dukes J.S. "Improving representation of photosynthesis in Earth System Models. New Phytologist 204(1), 12–14 (2014). [DOI:10.1111/nph.12972]

Rogers A, Medlyn B.E., Dukes J.S., Bonan G. et al. "A roadmap for improving representation of photosynthesis in Earth System Models." New Phytologist 213(1), 22–42 (2017). [DOI:10.1111/nph.14283]

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