Effects of carbon dioxide enrichment on a tallgrass ecosystem were monitored during the 1990 growing season. The chambers, CO{sub 2} delivery system, and data acquisition and control system were in place and operational by 4 April 1990. CO{sub 2} fumigation and data acquisition began on that date. Nitrogen fertilizer as ammonium nitrate was applied at a rate of 45 kg ha {sup -1} on 1 April to the N-fertilized plots. The chambers were 4.5 m in diameter and 4 m in height to allow for destructive sampling for biomass accumulation, leaf area determination, and for grazing esophageally-fistulated sheep. The experimental site was located in pristine Tallgrass Prairie north of/and adjacent to the Kansas State University campus. Vegetation on the site was a mixture of C3 and C4 species and was dominated by big bluestem (Andropogon geradii vitman) and indiangrass (Sorghastrum nutans (L.) Nash). Subdominants included Kentucky bluegrass (Poa pratensis L.), sideoats grama (Bouteloua curtipendula (Michx.) Torr.), and tall dropseed (Sporobolus asper var. asper (Michx.) Kunth). Members of the sedge family made up 5-10% of the composition. Principal forbs included western ragweed (Ambrosia psilostachya DC.), Louisiana sagewort (Artemesia ludoviciana Nutt.), and mayflower scurfpea (Psoralea tenuiflora var. floribunda (Nutt.) Rydb.). Average peak …