|Milchunas, D - COLORADO STATE UNIVERSITY|
|Parton, W - COLORADO STATE UNIVERSITY|
Submitted to: Ecological Applications
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: February 2, 2003
Publication Date: February 2, 2003
Citation: Morgan, J.A., Mosier, A.R., Milchunas, D.G., Lecain, D.R., Nelson, J.A., Parton, W.J. 2003. Co2 enhances productivity of the shortgrass steppe, alters species composition and reduced forage digestibility. Ecological Applications. 14:208-219. Technical Abstract: The impact of increasing atmospheric CO2 concentrations has been studied in a number of field experiments, but little information exists on the response of semi-arid rangelands to CO2, and even less on consequences for forage quality. This study was initiated to study the CO2 response of the shortgrass steppe. The experiment was conducted for five years on native vegetation at the USDA-ARS Central Plains Experimental Range in north-eastern Colorado. Three perennial grasses dominate the study site, Bouteloua gracilis (H.B.K.) Lag., a C4 grass, and two C3 grasses, Pascopyrum smithii (Rybd.) A. Love and Stipa comata Trin and Rupr. The three species comprise 88% of the aboveground phytomass. To evaluate responses to rising atmospheric CO2, we utilized six open-top chambers, three with ambient air, three with air CO2-enriched to 720 parts per million, and three unchambered controls. We found that elevated CO2 enhanced production of the shortgrass steppe throughout the study, with 38% greater aboveground phytomass harvested annually in elevated compared to ambient plots. The CO2-induced production response was driven by a single species, S. comata, and was due in part to greater seedling recruitment. The result was species movement towards a composition more typical of the mixed-grass prairie. Growth under elevated CO2 reduced the digestibility of all three dominant grass species, and was lowest in the only species to exhibit a CO2-induced production enhancement, S. comata. The results suggest that rising atmospheric CO2 may enhance production of lower quality, more drought sensitive forage in the shortgrass steppe.