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

Leaf gas exchange responses to elevated CO2 and N are presented for 13 perennial species, representing four functional groups: C-3 grasses, C-4 grasses, legumes, and nonleguminous forbs. Understanding how CO2 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 mu mol mol(-1)) CO2 concentrations (free-air CO2 enrichment), in combination with soil N treatments, for two growing seasons. All species, regardless of functional group, showed pronounced photosynthetic acclimation to elevated CO2, 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, and soil N supply did not interact for any leaf traits measured. Elevated CO2 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 CO2.