Background
With respect to one of the world's most important food crops, i.e., rice, the authors note that "doubts have been expressed whether the expected yield increases in response to increased CO2 could be sustained under high temperature regimes." Hence, they decided to see what would happen in subhumid Sri Lanka, where weekly maximum temperatures during both the maha (January to March) and yala (May to August) growing seasons typically range from 30-33°C.

What was done
De Costa et al. grew two crops of rice (Oryza sativa L., one in the maha season and one in the yala season) in open-top chambers maintained at atmospheric CO2 concentrations of either 363 or 567 ppm under normal field conditions at the Rice Research and Development Institute of Sri Lanka, measuring a number of meteorological and plant physiological parameters throughout both seasons, as well as total biomass production and grain yield at the times of final harvest.

What was learned
Among other things, the CO2-induced increase in total plant biomass at the time of final harvest was determined to be 23% in the maha season and 37% in the yala season, while final grain yields were enhanced by 24% and 39% in the maha and yala seasons, respectively.

What it means
"Based on the above results," in the words of the authors, "it is concluded that rice yields respond positively to increasing CO2 even at the higher range of growing temperatures" that were typical of their two experiments. What is more, the significant CO2-induced growth and yield increases of their study occurred in spite of the fact that air temperatures in the CO2-enriched chambers were an average of 1.6°C higher than air temperatures in the ambient-air chambers.