Leaf gas exchange responses of 13 prairie grassland species to elevated CO₂ and increased nitrogen supply

Summary 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 µmol 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 .