CO₂ENHANCES PRODUCTIVITY, ALTERS SPECIES COMPOSITION, AND REDUCES DIGESTIBILITY OF SHORTGRASS STEPPE VEGETATION

Abstract

Abstract. 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 mol/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.

Carbon dioxide enrichment alters plant community structure and accelerates shrub growth in the shortgrass steppe

“…3 A-C). Although the differences between C 3 and C 4 grasses were predicted based on differences in photosynthetic pathway, greater seedling recruitment of S. comata, a dominant C 3 grass and the only grass species to respond to CO 2 , was likely an important aspect of the C 3 reaction to CO 2 (10). Low growing season precipitation in 2000 ( Fig.…”

“…Whittaker's community association index is apparently able to detect CO 2 -induced changes in community structure because of its reliance on the relative contributions of particular species, whereas diversity, evenness, and richness, which are species-blind, may change more slowly. Increases in Whittaker's index were no doubt partially due to enhanced growth of S. comata (10) and A. frigida (Fig. 3D) but also were likely influenced by a number of other species that collectively became more dissimilar over time but when assayed individually did not display significant responses to CO 2 .…”

“…Rising atmospheric [CO 2 ] and predicted global change are expected to have an especially strong impact on water-limited regions like rangelands (6,7), with potential consequences for longestablished grazing practices. For instance, although grassland plant production often increases with rising atmospheric CO 2 , forage quality can decline because of lower N concentrations (8)(9)(10)(11) or because of an increased abundance of lower quality plant species (11).…”

“…These changes may affect not only the traditional goods and services we have come to expect from these lands but may alter their biodiversity as well. Our group previously evaluated the production responses of native Colorado shortgrass steppe vegetation to 5 years of growth (1997)(1998)(1999)(2000)(2001)) at elevated [CO 2 ] by using large open-top chambers (OTCs) (10). Here, we use data from this same experiment (http:// sgslter.colostate.edu/data/acquisitionplcy.htm) to examine how a doubling of CO 2 concentration for 5 years with OTCs placed over a native shortgrass steppe altered the botanical structure of this important semiarid grassland on the western edge of the North American Great Plains.…”

Climatic signals in tree-ring width and stable isotopes composition of <i>Pinus sylvestris</i> L. Growing in the industrialized area nearby Kędzierzyn-Koźle

“…Experimental results show that plants are able to increase their water-use efficiency (WUE) as CO 2 levels rise (Ehlelinger et al, 1993;Morison, 1993;Field et al, 1995;Gagen et al, 2011; , 2014;Sensuła, 2015;2016a). Increased atmospheric CO 2 concentration may stimulate plant growth, indirectly through reduced plant water consumption and hence slower soil moisture depletion, and directly through enhanced photosynthesis (Morgan et al, 2004). According to NASA (2016) the variability in the global surface temperature might be due to increase of global CO2 emissions.…”