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 gro wth and yield of crop plants. The objectives of this study were to determin e the interaction of N fertilization rates and atmospheric [CO2] on radiati on interception and radiation-use efficiency of rice (Oryza sativa L. cv. I R72) grown under tropical field conditions. Rice plants were grown inside o pen 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 elev ated (about 600 mu mol mol(-1) during the 1993 wet season and 700 mu mol mo l(-1) during the 1994 dry season) in combination with three levels of appli ed 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 increasi ng total absorbed N. Plant N requirement for radiation interception was sim ilar for rice grown under ambient [CO2] or elevated [CO2] treatments. The c onversion 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 a bout 2.5% resulted in lower RUE for plants grown with elevated [CO2] than f or plant grown at ambient [CO2]. Decreased leaf N with increased [CO2], the refore decreased RUE of rice plants grown at elevated [CO2]. When predictin g responses of rice to elevated [CO2], RUE should be adjusted with a decrea se in leaf N.