What was done
The authors grew five pasture species [Festuca arundinacea (perennial grass), Lolium perenne (perennial grass), Phalaris aquatica (perennial grass), Poa annua (annual grass), and Trifolium repens (perennial legume)] for approximately one month in controlled environment chambers receiving atmospheric CO2 concentrations of 350 and 700 ppm.  In addition, plants were simultaneously grown at 18 and 28°C to determine the interactive effects of elevated CO2 and temperature on photosynthesis and growth in these species.

What was learned
Elevated CO2 stimulated photosynthetic rates in all five species by an average of 36 and 70% at 18 and 28°C, respectively.  This increase in carbon accumulation undoubtedly contributed to increases in biomass production that averaged 8 and 95% for all species at the same respective temperatures.  Thus, the beneficial effects of elevated CO2 on photosynthesis and growth in these five pasture species increased with increasing air temperature.

What it means
As the CO2 content of the air continues to rise, it is likely that these and other pasture species will exhibit increased rates of photosynthesis and greater biomass production.  And if air temperature rises concurrently, the growth-enhancing benefits of the rising atmospheric CO2 concentration will likely be even greater.  The thought of it almost makes one want to wish for global warming!