What was done
The authors grew five fast-growing native annual species in glasshouses with two different combinations of CO2 (ambient or ambient plus 340 ppm) and temperature (ambient or ambient plus 3°C) for eight weeks to assess their growth responses to elevated CO2 and temperature.

What was learned
Elevated CO2 significantly increased photosynthetic rates by 18-36% for all species, regardless of growth temperature, for the entire eight-week experiment.  The persistence of this photosynthetic enhancement led to total plant biomass increases for CO2-enriched plants that were, on average, 25% greater than those of control plants grown in ambient CO2.  Elevated CO2 and elevated temperature, in combination, had few significant interactive effects on growth, although the CO2 growth response was generally larger at elevated, rather than at ambient, temperature.

What it means
As the CO2 content of the air increases, fast-growing native annual species, such as the five studied in this paper, will likely respond positively by increasing their photosynthetic rates and total biomass, regardless of any concomitant rise in air temperature.