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Title: Simulating carbon dioxide effects on range plant growth and water use with GPFARM-Range model

Author
item QI, ZHIMING - McGill University - Canada
item Morgan, Jack
item McMaster, Gregory
item Ahuja, Lajpat
item Derner, Justin

Submitted to: Climatic Change
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/6/2015
Publication Date: 8/1/2015
Citation: Qi, Z., Morgan, J.A., McMaster, G.S., Ahuja, L.R., Derner, J.D. 2015. Simulating carbon dioxide effects on range plant growth and water use with GPFARM-Range model. Climatic Change. 68(5):423-431. doi:10.1016/j.rama.2015.07.007.

Interpretive Summary: Steadily rising CO2 in Earth’s atmosphere has the potential to increase plant biomass production and reduce plant transpiration in rangelands under certain conditions. In this study, we added algorithms for computing changes in range plant biomass growth and stomatal resistance under elevated [CO2] to the GPFARM-Range model, a newly developed stand-alone software package for rangeland management. The GPFARM-Range model was tested against 5-yrs (1997-2001) of soil water and biomass data from an open-top chamber CO2 enrichment field experiment conducted in a shortgrass steppe dominated by C3 and C4 grasses in northern Colorado. Simulated results for both peak standing crop biomass and soil water for both ambient and elevated [CO2] treatments were predicted within ± 10% of the measured values. The model captured the observed trend of increased C3 grass biomass and reduced plant transpiration under elevated [CO2].

Technical Abstract: Steadily rising CO2 in Earth’s atmosphere has the potential to increase plant biomass production and reduce plant transpiration in rangelands under certain conditions. Incorporating results from field CO2-enrichment experiments into process-based simulation models enhances our ability to consider this potential in projections of climate change impacts on rangelands. In this study, we added algorithms for computing changes in range plant biomass growth and stomatal resistance under elevated [CO2] to the GPFARM-Range model, a newly developed stand-alone software package for rangeland management. The biomass growth and stomatal resistance algorithms were adopted from the SPUR2 and EPIC models, respectively. The GPFARM-Range model was tested against 5-yrs (1997-2001) of soil water and biomass data from an open-top chamber CO2 enrichment field experiment conducted in a shortgrass steppe dominated by C3 and C4 grasses in northern Colorado. Simulated results for both peak standing crop biomass and soil water for both ambient and elevated [CO2] treatments had a percent bias within ± 10%, Nash-Sutcliffe efficiency = 0.5, and index of agreement > 0.70. The model also captured the observed trend of increased C3 grass biomass and reduced plant transpiration under elevated [CO2]. The model was used to evaluate the separate effectiveness of elevated [CO2] on plant growth rate (C3 grasses only) and stomatal resistance (both C3 and C4 grasses). Increased biomass with elevated [CO2] was almost evenly promoted by increased growth rate and stomatal resistance. The results indicate the algorithms used to simulate the impacts of elevated [CO2] on range plant growth and water use are reliable and can be used to evaluate rangeland production for future increases in [CO2]. However, underestimated reduction in plant transpiration by the model needs further study. Keywords: GPFARM-Range, carbon dioxide, growth rate, stomatal resistance, modeling Abbreviations: GPFARM-Range, Great Plains Framework for Agricultural Resource Management in Rangelands; SPUR, Simulation of Production and Utilization of Rangelands; EPIC, Environmental Policy and Integrated Model; PBIAS, percent bias; NSE, Nash-Sutcliffe model efficiency; D, index of agreement; RMSD, root mean squared deviation.