Photosynthesis, growth and density for the dominant species in a CO₂-enriched grassland

Avena barbata in the field showed little evidence of photosynthetic downregulation with elevated CO₂ at the end of the growing season (differences between treatments <10%). Glasshouse studies also showed little evidence for downregulation of photosynthesis measured at various light and intercellular CO₂ concentrations. Although specific leaf mass (leaf mass per unit leaf area) for Avena increased 20% in the field with elevated CO₂, leaf nitrogen concentrations decreased 25%, resulting in an 11% reduction in leaf N on a leaf-area basis. For the relatively wet 1993 growing season, A. barbata increased its size and reproduction c30% in elevated CO₂, with a 21% decrease in population density. For the relatively dry 1994 season density was almost doubled in elevated CO₂, but increases in individual size and reproduction with CO₂ were small (6-18%). The primary effect of CO₂ in the drier year appears to have been greater Avena survival, rather than increased individual size. -from Authors