Warming Restricts Rice Yield Gains Brought by Higher CO2 Concentrations: Study

Japan's National Institute for Agro-Environmental Sciences published on March 7, 2013, the results of a study on the effects of higher atmospheric CO2 concentrations and air temperatures on rice harvest yields. The results show that higher air temperatures restrict increases in harvest yields brought by higher CO2 concentrations.

The data were obtained from free-air CO2 enrichment (FACE) experiments conducted in collaboration with the Tohoku Agricultural Research Center of the National Agriculture and Food Research Organization and other institutes. Harvest yields were compared with rice cultivated in outdoor paddy fields where atmospheric CO2 concentrations were artificially raised by around 50 percent (200 parts per million). Experiments carried out in Iwate prefecture from 1998 to 2008 and in Ibaraki prefecture from 2010 to 2011 exhibited average air temperatures of 18.4 to 21.4 degrees Celsius and 24.2 to 25.2 degrees Celsius, respectively.

By comparing the harvest yields of the same rice variety grown in these two locations, it was found that yields were on average 13 percent higher than normal CO2 concentrations. However, due to inter-year variations in temperature conditions, the increase in harvest yield caused by rising CO2 concentrations may not be as large as the predicted values on a warming planet. The results should help scientists to develop new rice varieties that are adapted to environments with higher CO2 concentrations in the future.