Response of rice yield traits to elevated atmospheric CO2 concentration and its interaction with cultivar, nitrogen application rate and temperature: A meta-analysis of 20 years FACE studies.

The Free Air CO2 Enrichment (FACE) facility simulates future high CO2 environment in an open field, and is considered the best approach to assess the actual response of crop production to climate change. This meta-analysis synthesizes all studies conducted under FACE conditions on rice yield response to elevated atmospheric CO2 concentration ([CO2]) and its interaction with cultivar, nitrogen application rate and temperature. On average, elevated [CO2] enhanced rice yield by 16.2%, which resulted from positive response of each yield component. The yield enhancement by elevated [CO2] of hybrid rice (24.7%) was significantly greater than conventional rice (14.2%), and among conventional rice cultivars, indica rice had a larger yield response (20.4%) than japonica rice (12.7%). The superior performance of hybrid and indica rice under FACE conditions was mainly attributed to the larger increase in spikelet density. The response of rice yield to elevated [CO2] varied with nitrogen supply. The maximum increase of 21.1% occurred at the nitrogen application rate of 21-30 g m-2. Both insufficient and excess nitrogen supply negate yield increase by FACE but through different approaches. Elevated [CO2] increased rice yield by 16.7% at ambient temperature but only 10.1% at elevated temperature (1-2 °C); The smaller yield increase at elevated temperature was due to the negative response of filled grain percentage and grain mass. In conclusion, atmospheric CO2 concentration projected in the middle of this century will enhance rice yield mainly through the increase of spikelet density, whereas the magnitude of CO2 fertilizer effect will be affected by the cultivar, nitrogen application rate and temperature.