Atmospheric CO2 concentration effects on N partitioning and fertilizer N recovery in field grown rice (Oryza sativa L.)

Lowland rice (Oryza sativa L.) responds positively to increased atmospheric CO2 concentration. However, the efficiency of the canopy depends on the N status of the plant, which could vary with the change in uptake and partitioning of N with increased atmospheric CO2. A field experiment was conducted at the International Rice Research Institute (IRRI) to determine changes in N requirement of the rice crop and to propose suitable management strategies to overcome tissue N dilution with increased CO2 concentration. Rice variety IR72 was grown inside open top chambers at ambient (about 350 μmol mol−1) or elevated (700 μmol mol−1) atmospheric CO2 in combination with three levels of applied N (0, 90, or 200 kg N ha−1). Rooting of rice was linearly related to tillering, and the relationship did not change with CO2 concentrations, but with age of the crop. When adequate N was not supplied, rice plants grown at high CO2 became inferior to plants grown at ambient CO2. N uptake and fertilizer N recovery was higher in plants grown in high CO2 until maximum tillering, but the partitioning of N towards leaves decreased by 9%. Acclimation to high CO2 by rice may, therefore, be dependent on the N uptake. Increased N uptake under high CO2 environment was related to its larger root system, which was due to increased unproductive tillering. This suggests that if tillering is limited, rice plants at high CO2 may suffer from N limitation due to changes in both uptake and partitioning. It is concluded that management of the rice crop grown at high atmospheric CO2 should be different to that under current conditions.