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The Responses of Three C3 Grasses to Elevated CO2 While Competing for Light
Teyssonneyre, F., Picon-Cochard, C. and Soussana, J.F.  2002.  How can we predict the effects of elevated CO2 on the balance between perennial C3 grass species competing for light?  New Phytologist 154: 53-64.

What was done
The authors grew three C3 grasses (Lolium perenne, Festuca arundinacea and Holcus lanatus) as monocultures and two-species mixtures for five months within plastic tunnels maintained at atmospheric CO2 concentrations of 350 and 700 ppm.  In addition, the grasses were cut either frequently or infrequently to stimulate competition for light, in order to determine if competition for light influences the growth response of the grasses to elevated CO2.

What was learned
Cutting frequency did not interact with elevated CO2 in any of the monocultures, where, on average, elevated CO2 increased total aboveground biomass by 22%, 22% and 4% in Festuca, Holcus and Lolium, respectively.  In the two-species mixtures, however, cutting frequency did impact the percentage of Lolium present.  In the Lolium x Festuca mixture, the percentage of Lolium present was not affected by elevated CO2 under the frequent cutting regime; but infrequent cutting caused a 22% CO2-induced reduction in its presence.  Similarly, elevated CO2 caused 30% and 67% reductions in the amount of Lolium present in mixtures with Holcus under frequent and infrequent cutting regimes, respectively.

What it means
As the CO2 concentration of the air increases, competition for light among certain C3 grasses likely will play a role in their ability to respond to the additional CO2 in terms of biomass production.  Specifically, under elevated CO2 concentrations, Festuca and Holcus may be able to outcompete Lolium for available light (in terms of vertical leaf area development) in infrequently cut regimes, which may consequently allow the former species to grow more robustly in mixed stands under such conditions.

Reviewed 30 October 2002