TY - JOUR T1 - Biomass production and species composition change in a tallgrass prairie ecosystem after long-term exposure to elevated atmospheric CO2 JF - Global Change Biology Y1 - 1999 A1 - Owensby, C.E. A1 - J.M. Ham A1 - Alan K. Knapp A1 - Auen, L.M. KW - tallgrass prairie AB - To determine the long-term impact of elevated CO2 on primary production of native tallgrass prairie, we compared the responses of tallgrass prairie at ambient and twice-ambient atmospheric CO2 levels over an 8-year period. Plots in open-top chambers (4.5 m diameter) were exposed continuously (24 h) to ambient and elevated CO2 from early April to late October each year. Unchambered plots were monitored also. Above-ground peak biomass was determined by clipping each year in early August, and root growth was estimated by harvesting roots from root ingrowth bags. Plant community composition was censused each year in early June. In the last 2 years of the study, subplots were clipped on 1 June or 1 July, and regrowth was harvested on 1 October. Volumetric soil water content of the 0–100 cm soil layer was determined using neutron scattering, and was generally higher in elevated CO2 plots than ambient. Peak above-ground biomass was greater on elevated CO2 plots than ambient CO2 plots with or without chambers during years with significant plant water stress. Above-ground regrowth biomass was greater under elevated CO2 than under ambient CO2 in a year with late-season water stress, but did not differ in a wetter year. Root ingrowth biomass was also greater in elevated CO2 plots than ambient CO2 plots when water stress occurred during the growing season. The basal cover and relative amount of warm-season perennial grasses (C4) in the stand changed little during the 8-year period, but basal cover and relative amount of cool-season perennial grasses (C3) in the stand declined in the elevated CO2 plots and in ambient CO2 plots with chambers. Forbs (C3) and members of the Cyperaceae (C3) increased in basal cover and relative amount in the stand at elevated compared to ambient CO2. Greater biomass production under elevated CO2 in C4-dominated grasslands may lead to a greater carbon sequestration by those ecosystems and reduce peak atmospheric CO2 concentrations in the future. VL - 5 ER - TY - JOUR T1 - Water vapor fluxes and their impact under elevated CO2 in a C4 tallgrass prairie JF - Global Change Biology Y1 - 1997 A1 - Owensby, C.E. A1 - J.M. Ham A1 - Alan K. Knapp A1 - D. Bremer A1 - Auen, L.M. KW - tallgrass prairie AB - We measured leaf-level stomatal conductance, xylem pressure potential, and stomate number and size as well as whole plant sap flow and canopy-level water vapour fluxes in a C4-tallgrass prairie in Kansas exposed to ambient and elevated CO2. Stomatal conductance was reduced by as much as 50% under elevated CO2 compared to ambient. In addition, there was a reduction in stomate number of the C4 grass, Andropogon gerardii Vitman, and the C3 dicot herb, Salvia pitcheri Torr., under elevated CO2 compared to ambient. The result was an improved water status for plants exposed to elevated CO2 which was reflected by a less negative xylem pressure potential compared to plants exposed to ambient CO2. Sap flow rates were 20 to 30% lower for plants exposed to elevated CO2 than for those exposed to ambient CO2. At the canopy level, evapotranspiration was reduced by 22% under elevated CO2. The reduced water use by the plant canopy under elevated CO2 extended the photosynthetically-active period when water became limiting in the ecosystem. The result was an increased above- and belowground biomass production in years when water stress was frequent. VL - 3 ER - TY - CHAP T1 - Ecosystem level responses of tallgrass prairie to elevated CO2 T2 - Carbon Dioxide and Terrestrial Ecosystems Y1 - 1996 A1 - Owensby, C.E. A1 - J.M. Ham A1 - Alan K. Knapp A1 - C. W. Rice A1 - Coyne, P.I. A1 - Auen, L.M. ED - Koch, G.W ED - Mooney, H.A. KW - tallgrass prairie JF - Carbon Dioxide and Terrestrial Ecosystems PB - Academic Press CY - London ER - TY - JOUR T1 - Biomass production in a tallgrass prairie ecosystem exposed to ambient and elevated CO2 JF - Ecological Applications Y1 - 1993 A1 - Owensby, C.E. A1 - Coyne, P.I. A1 - Ham, J.M. A1 - Auen, L.M. A1 - Alan K. Knapp KW - Aboveground biomass KW - Andropogon gerardii KW - Carbon dioxide KW - elevated CO2 KW - kansas KW - Poa pratensis KW - Root biomass KW - tallgrass prairie KW - water-use efficiency KW - xylem pressure potential VL - 3 ER - TY - JOUR T1 - Effects of dormant-season herbage removal on Flint Hills rangeland JF - Journal of Range Management Y1 - 1988 A1 - Auen, L.M. A1 - Owensby, C.E. AB -

Intensive-early stocking in the Kansas Flint Hills has greatly increased livestock production efficiency. The potential grazing of regrowth on intensive-early stocked Flint Hills pastures was studied by monthly mowing to 5-cm height form October to April, 1983-1985. Those treatments had no effect on total nonstructural carbohydrates (TNC) in Andropogon gerardii Vitman rhizomes or on herbage production the following seasons. Since there was no reduction in herbage yield for any mowing date, cattle producers can apparently restock IES pastures after 1 October. Key Words: total nonstructural carbohydrates, Andropogon gerardii , winter removal, near-infrared reflectance spectroscopy

VL - 41 ER - TY - THES T1 - Effects of dormant season herbage removal on Flint Hills rangeland. II. Near-infrared reflectance spectroscopy analysis of total nonstructural carbohydrates in big bluestem rhizomes Y1 - 1987 A1 - Auen, L.M. KW - remote sensing PB - Kansas State University CY - Manhattan, KS VL - MS Thesis UR - http://krex.k-state.edu/dspace/handle/2097/16786 ER -