Global atmospheric CO2 concentration is increasing, likely increasing the p
roductivity of crops as higher CO2 enhances plant photosynthesis. Responsiv
eness to nitrogen supply is an essential trait of modem rice cultivars, and
may play a role in the response of rice cultivars to CO2. To determine the
relationship between these two important production variables on young ric
e plants, seedlings of Oryza sativa L. 'IR72' and 'KDML 105' were exposed f
or 28 days after sowing to CO2 levels of 373, 545, 723 and 895 mu molmoI(-1
), and 3 levels of nitrogen fertility. There were large increases in leaf C
O2 assimilation and biomass production whereas leaf nitrogen concentration
dropped sharply as CO2 increased from 373 to 545 mu mol mol(-l), with littl
e additional effect from higher levels of CO2. Root and shoot biomass, and
tiller number per plant increased with increasing nitrogen supply and with
increasing atmospheric CO2 concentration. The biomass response to CO2 was s
light at low N supply, but became dramatically greater as the N supply incr
eased. Mean root/shoot ratio increased slightly as atmospheric CO2 concentr
ation increased, but decreased sharply as nitrogen fertility rate increased
. These results suggest that careful attention to nitrogen fertilization wi
ll be necessary for rice fanning to get the full benefit of any future incr
eases in atmospheric CO2. (C) 1999 Published by Elsevier Science B.V. All r
ights reserved.