Effects of nitrogen nutrition on responses of rice seedlings to carbon dioxide

Abstract

Global atmospheric CO 2 concentration is increasing, likely increasing the productivity of crops as higher CO 2 enhances plant photosynthesis. Responsiveness to nitrogen supply is an essential trait of modern rice cultivars, and may play a role in the response of rice cultivars to CO 2. To determine the relationship between these two important production variables on young rice plants, seedlings of Oryza sativa L. `IR72' and `KDML 105' were exposed for 28 days after sowing to CO 2 levels of 373, 545, 723 and 895 μmol mol −1, and 3 levels of nitrogen fertility. There were large increases in leaf CO 2 assimilation and biomass production whereas leaf nitrogen concentration dropped sharply as CO 2 increased from 373 to 545 μmol mol −1, with little additional effect from higher levels of CO 2. Root and shoot biomass, and tiller number per plant increased with increasing nitrogen supply and with increasing atmospheric CO 2 concentration. The biomass response to CO 2 was slight at low N supply, but became dramatically greater as the N supply increased. Mean root/shoot ratio increased slightly as atmospheric CO 2 concentration increased, but decreased sharply as nitrogen fertility rate increased. These results suggest that careful attention to nitrogen fertilization will be necessary for rice farming to get the full benefit of any future increases in atmospheric CO 2.