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CO 2 ENHANCES PRODUCTIVITY, ALTERS SPECIES COMPOSITION, AND REDUCES DIGESTIBILITY OF SHORTGRASS STEPPE VEGETATION
Author(s) -
Morgan Jack A.,
Mosier Arvin R.,
Milchunas Daniel G.,
LeCain Daniel R.,
Nelson Jim A.,
Parton William J.
Publication year - 2004
Publication title -
ecological applications
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.864
H-Index - 213
eISSN - 1939-5582
pISSN - 1051-0761
DOI - 10.1890/02-5213
Subject(s) - bouteloua gracilis , rangeland , stipa , steppe , grassland , agronomy , perennial plant , grazing , productivity , forage , vegetation (pathology) , ecology , biology , environmental science , medicine , pathology , economics , macroeconomics
The impact of increasing atmospheric CO 2 concentrations has been studied in a number of field experiments, but little information exists on the response of semiarid rangelands to CO 2 , or on the consequences for forage quality. This study was initiated to study the CO 2 response of the shortgrass steppe, an important semiarid grassland on the western edge of the North American Great Plains, used extensively for livestock grazing. The experiment was conducted for five years on native vegetation at the USDA‐ARS Central Plains Experimental Range in northeastern Colorado, USA. Three perennial grasses dominate the study site, Bouteloua gracilis , a C 4 grass, and two C 3 grasses, Pascopyrum smithii and Stipa comata . The three species comprise 88% of the aboveground phytomass. To evaluate responses to rising atmospheric CO 2 , we utilized six open‐top chambers, three with ambient air and three with air CO 2 enriched to 720 μmol/mol, as well as three unchambered controls. We found that elevated CO 2 enhanced production of the shortgrass steppe throughout the study, with 41% greater aboveground phytomass harvested annually in elevated compared to ambient plots. The CO 2 ‐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 toward a composition more typical of the mixed‐grass prairie. Growth under elevated CO 2 reduced the digestibility of all three dominant grass species. Digestibility was also lowest in the only species to exhibit a CO 2 ‐induced production enhancement, S. comata . The results suggest that rising atmospheric CO 2 may enhance production of lower quality forage and a species composition shift toward a greater C 3 component.