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Keywords:

  • elevated CO2;
  • nitrogen availability;
  • photosynthetic acclimation;
  • functional groups;
  • prairie grassland;
  • stomatal conductance

Summary

  •  Leaf gas exchange responses to elevated CO2 and N are presented for 13 perennial species, representing four functional groups: C3 grasses, C4 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 µmol 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 C3 grasses, +8% in forbs, +7% in legumes and −2% in C4 grasses. The effects of CO2 and soil N supply did not interact for any leaf traits measured. Elevated CO2 consistently decreased stomatal conductance (gs) leading to 40% increase in A/gs.
  •  This substantial acclimation of photosynthesis was greater in magnitude than in most field studies, and was associated with the combined effects of decreased gs and decreased leaf N concentrations in response to growth under elevated CO2.