Atmospheric carbon dioxide and fertilizer nitrogen effects on radiation interception by rice

In order to predict the potential impacts of global change, it is important to understand the impact of increasing global atmospheric [CO2] on the growth and yield of crop plants. The objectives of this study were to determine the interaction of N fertilization rates and atmospheric [CO2] on radiation interception and radiation-use efficiency of rice (Oryza sativa L. cv. IR72) grown under tropical field conditions. Rice plants were grown inside open top chambers in a lowland rice field at the International Rice Research Institute in the Philippines at ambient (about 350 mu mol mol(-1)) or elevated (about 600 mu mol mol(-1) during the 1993 wet season and 700 mu mol mol(-1) during the 1994 dry season) in combination with three levels of applied N (0, 50 or 100 kg N ha(-1) in the wet season; 0, 90 or 200 kg N ha(-1) in the dry season). Light interception was not directly affected by [CO2], but elevated [CO2] indirectly increased light interception through increasing total absorbed N. Plant N requirement for radiation interception was similar for rice grown under ambient [CO2] or elevated [CO2] treatments. The conversion efficiency of intercepted radiation to dry matter, radiation-use efficiency (RUE), was about 35% greater at elevated [CO2] than at ambient [CO2]. The relationship between leaf N and RUE was curvilinear. At ambient [CO2], RUE was fairly stable across levels of leaf N, but leaf N less than about 2.5% resulted in lower RUE for plants grown with elevated [CO2] than for plant grown at ambient [CO2]. Decreased leaf N with increased [CO2], therefore decreased RUE of rice plants grown at elevated [CO2]. When predicting responses of rice to elevated [CO2], RUE should be adjusted with a decrease in leaf N.