Owensby et al. (1993) reported on N concentrations in A. gerardii, P. pratensis, and forb aboveground biomass in tallgrass prairie exposed to ambient and elevated CO₂ over the 3-year period. N concentration of root ingrowth bag biomass was also measured. Total N in above- and belowground biomass was calculated as a product of concentration and peak biomass by species groups. N concentration in A. gerardii and forb aboveground biomass was lower and total N higher in elevated CO₂ plots than in ambient CO₂ plots. N concentration in P. pratensis aboveground biomass was lower in elevated CO₂ plots than in ambient, but total N did not differ among treatments in 2 of 3 years. In 1990, N concentration in root ingrowth bag biomass was lower and total N greater in elevated CO₂ than in ambient CO₂ plots. Root ingrowth bag biomass N concentration did not differ among treatments in 1991, but total N in root ingrowth bag biomass was greater in elevated CO₂ plots than in ambient CO₂ plots. The impact of elevated CO₂ on decomposition of aboveground biomass and soil microbial processes were also measured. Rice et al. (1994) determined the effects of elevated CO₂ in unfertilized and N-fertilized plots on amount of carbon and nitrogen stored in soil organic matter and microbial biomass and microbial activity in 1991 and 1992. The data were taken on the plots that had been exposed to elevated and ambient CO₂ since 1989 for the unfertilized plots and since 1990 for the fertilized. Soil organic C and N significantly increased after three seasons under enriched atmospheric CO₂. In 1991, a dry year, CO₂ enrichment significantly increased microbial biomass C and N compared to ambient, but in 1992, a wet year, microbial biomass C and N did not differ among CO₂ treatments. Added N increased microbial C and N and stimulated microbial activity under CO₂ enrichment. Microbial activity was consistently greater under CO₂ enrichment probably as a result of better soil water conditions. Ratios of microbial to organic C and N did not differ among treatments. Increased microbial N with CO₂ enrichment was another indication that plant production may become limited by N availability. In order to determine if the soil system could compensate for the limited N by increasing the labile pool to support increased plant production with elevated atmospheric CO₂, longer-term studies are needed to determine how tallgrass prairie will respond to increased C input. Because translocation of N in late-season from the aboveground biomass to belowground storage made aboveground litter similar in tissue chemistry, decomposition of surface litter was unaffected by CO₂ treatment (Kemp et al. 1994). They collected standing dead and green foliage litter from A. gerardii (C₄), S. nutans (C₄), and P. pratensis (C₃) plants that had been grown under twice-ambient or ambient CO₂ and with or without nitrogen fertilization. The litter was placed in mesh bags on the soil surface of adjacent prairie and allowed to decay over a 2-year period. Litter bags, retrieved at intervals, showed that the CO₂ treatment had a relatively minor effect on the initial chemical composition of the litter or its subsequent rate of decay. However, there was a large difference among species in litter decomposition. P. pratensis leaf litter decayed more rapidly, had higher total N & P, and a different initial carbon chemistry than the C₄ grasses. These differences suggest that there could be an indirect effect of CO₂ on decomposition and nutrient cycling by way of CO₂-induced changes in species composition. The increased microbial N, higher soil C content of the upper soil layer, and the increased microbial respiration with N addition all indicate that there is a reduction in soil organic matter decomposition under elevated CO₂. Those data support the contention that, in the long term, N limitation may slow the biomass production response to elevated CO₂. Because surface litter chemistry does not appear to differ between ambient and elevated CO₂ treatments, it is not likely higher atmospheric CO₂ will cause significant change in surface litter decomposition.