Increasing atmospheric CO2 concentrations and climatic change will have significant effects on the ecology of grasslands. This paper evaluates results from four CO2 enrichment studies in contrasting grasslands. A Swiss study investigates the effects of elevated CO2 (600 μL L-1 CO2) on perennial ryegrass (Lolium perenne L.) and white clover (Trifolium repens L), a New Zealand study examines how elevated CO2 (475 μL L-1 CO2) affects a botanically diverse pasture, and studies in the Kansas tallgrass prairie and the Colorado shortgrass steppe investigate the effects of an approximate doubling of CO2 in native grasslands. Productivity in all four grasslands was enhanced at elevated CO2, with the largest relative increases occurring in dry years on the shortgrass steppe (71%) and on the tallgrass prairie (36%). Nitrogen additions, whether from fertilizer or legumes, enhanced the capability of these grasslands to respond to CO2, and legumes were among the most competitive plant types in the Swiss and New Zealand grasslands under elevated CO2. No evidence was found to support the notion that C3 grasses were more competitive under elevated CO2 compared to C4 grasses. The results suggest that CO2 enrichment and global warming will have important impacts on grasslands
