Leaf gas exchange responses of 13 prairie grassland species to elevated CO 2 and increased nitrogen supply

• Leaf gas exchange responses to elevated CO 2 and N are presented for 13 perennial species, representing four functional groups: C 3 grasses, C 4 grasses, legumes, and nonleguminous forbs. Understanding how CO 2 and N effects interact is important to predict plant community response to global change. • Plants were field-grown in monoculture under current ambient and elevated (560 μ mol mol − 1 ) CO 2 concentrations (free-air CO 2 enrichment), in combination with soil N treatments, for two growing seasons. • All species, regardless of functional group, showed pronounced photosynthetic acclimation to elevated CO 2 , resulting in minimal stimulation of photosynthesis ( A ) averaging +15% in C 3 grasses, +8% in forbs, + 7% in legumes and − 2% in C 4 grasses. The effects of CO 2 and soil N supply did not interact for any leaf traits measured. Elevated CO 2 consistently decreased stomatal conductance ( g s ) leading to 40% increase in A / g s . • This substantial acclimation of photosynthesis was greater in magnitude than in most field studies, and was associated with the combined effects of decreased g s and decreased leaf N concentrations in response to growth under elevated CO 2 .