Effects of a CO2-enriched atmosphere on the growth and competitive interaction of a C3 and a C4 grass.

Festuca elatior L., C3, and Sorghum halepense (L.) Persoon, C4, were grown in mixed and unmixed cultures under 350 and 600 ppm CO2 for 112 days. High CO2 levels stimulated increases of total dry weight and leaf surface area in Festuca despite unfavorably high temperatures. In Sorghum, delay of leaf senescence and of floral initiation was attributed to high CO2 concentrations. Growth of unmixed cultures of Sorghum under 600 ppm CO2 was relatively poor because of an apparent interaction of high CO2 with self-shading. All instances of culturexCO2 interactions are offered in supported of the hypothesis that elevated CO2 levels will effect the competitive interaction of C3 and C4 species. Peak net assimilation rates of C3 and C4 plants were seasonally separated at 350 ppm CO2 but coincided at 600 ppm. Based on our observations of Festuca and Sorghum, we project that global CO2 enrichment may alter competitive balance between C3 and C4 plants and subsequently affect seasonal niche separation, species distribution patterns, and net primary production within mixed communities.