Submitted to: Society for Range Management Meeting Abstracts
Publication Type: Abstract Only
Publication Acceptance Date: 12/10/2007
Publication Date: 2/18/2008
Citation: Polley, H.W., Fay, P.A. 2008. Change is in the air: impacts of the historical and predicted increase in atmospheric CO2 on pasture and prairie. In: Proceedings of the Society for Range Management, January 26-31, 2008, Louisville, Kentucky. 2008 CDROM.
Technical Abstract: The concentration of carbon dioxide (CO2) gas in the atmosphere has increased by almost 40% since the beginning of the Industrial Revolution and is predicted to reach double the pre-Industrial concentration within 50 years. By stimulating leaf photosynthesis and reducing stomatal conductance to water, CO2 enrichment should increase growth of forage plants. But, rising CO2 also may alter the competitive balance between forage and non-forage species and reduce forage quality. We use results from two CO2 experiments in central Texas, the first on pasture dominated by an introduced C4 grass and the second on plots planted to tallgrass prairie species, to compare the responses of pasture and prairie plants to CO2 at pre-Industrial to elevated concentrations. CO2 enrichment increased aboveground biomass of the dominant pasture grass during the first year of CO2 exposure, but increased production of C4 prairie grasses only on the least fertile of the three soils studied. Benefits of greater grass production were partly offset by a decline in forage quality (tissue N concentration) on both prairie and pasture. CO2 enrichment amplified a shift in pasture vegetation from dominance by grasses to co-dominance between grasses and perennial forbs. By contrast, CO2 enrichment of prairie plants increased biomass of perennial forbs only on the most fertile of three soils. Rising CO2 likely is boosting the productive potential of both native and introduced C4 forage grasses. Benefits of greater forage production may be reduced or even eliminated by a decrease in forage N concentration and by the greater responsiveness of forbs than grasses to CO2, however.