Submitted to: Ecological Modeling
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/1/1996
Publication Date: N/A
Citation: Interpretive Summary: Atmospheric carbon dioxide concentrations (C02) have been incrasing for more than a century, and are projected to double over present-day concen- trations of approximately 360 parts per million (ppm) by the end of the next century. Because C02 is a greenhouse gas, and as such can trap some of the sun's energy in the earth's atmosphere, these increasing C02 concentra- -tions are predicted to lead to global warming, and also alter precipitatio patterns around the world. Experiments are being conducted in major ecosys- tems to determine how elevated C02 and global change will influence their ecology, but these studies are very expensive to implement, leaving many possible global change scenarios superficially analyzed in experiments. Some of these knowledge gaps may be bridged through computer modeling exer- cises that attempt to simulate the ecosystem and impact of global change on its ecology. This study was undertaken to test the Grassland Ecosystem Model's (GEM) capability to represent the response of native shortgrass steppe grasses to elevated C02 and variable temperature and water supply. The GEM applied to the results of an experiment in which native grasses and soils from the Central Great Plains were grown in large, indoor growth chamber rooms maintained at two C02 concentrations, variable temperature and three water regimes. GEM successfully predicted enhanced productivity and reduced N concentration of the native grasses at elevated C02. It was also able to correctly represent complicated interactions and feedbacks that mediate ecological responses of this grassland to global change. The results of this modeling exercise are encouraging, as they suggest that this approach to understanding how complex ecosystems respond to global change will be useful in supplementing our experimental data sets.
Technical Abstract: Ecological responses to C02 enrichment and climate change are expressed at several interacting levels: photosynthesis and stomatal movement at the leaf level, energy and gas exchanges at the canopy level, photosynthetic allocation and plant growth at the plant level, and water budget and nitro- gen cycling at the ecosystem level. Version GEM2 of the Grassland Ecosystem mModel linked biochemical, ecophysiological and ecosystem processes in a hierarchical approach. The model included biochemical level mechanisms of C3 and C4 photosynthetic pathways to represent direct effects of C02 on plant growth, mechanistically simulated biophysical processes which control interactions between the ecosystem and the atmosphere, and linked with detailed biogeochemical process submodels. The model was tested using two- year full factorial (C02, temperature and precipitation) growth chamber data for the grasses Pascopyrum smithii (C3) and Bouteloua gracilis (C4). The C3-C4 photosynthesis submodels fitted the measured photosynthesis data from both the C3 and C4 species subjected to different C02, temperature and precipitation conditions. The whole GEM2 model accurately fitted plant biomass dynamics and plant N content data over a wide range of temperature, precipitation and atmospheric C02 concentration. Both data and stimulation results showed that elevated C02 enhanced plant biomass production in both P. smithii (C3) and B. gracilis (C4). The enhancement of shoot production by elevated C02 varied with temperature and precipitation.