INTRASPECIFIC VARIATION IN THE RESPONSE OF RICE (ORYZA-SATIVA L) TO INCREASED CO2 AND TEMPERATURE - GROWTH AND YIELD RESPONSE OF 17 CULTIVARS

Seventeen rice (Oryza sativa L.) cultivars of contrasting ecosystems a nd origins were exposed to two CO2 concentrations (373 [ambient] and 6 64 mu l l(-1) CO2 [elevated]) at two different day/night temperatures (29/21 degrees C and 37/29 degrees C) in glasshouses at the Internatio nal Rice Research Institute phytotron during the dry seasons of 1994 a nd 1995, Growth at elevated CO2 (as determined by total plant biomass at maturity) increased by an average of 70% and 22%, respectively, for all cultivars for growth temperatures of 29/21 degrees C and 37/29 de grees C relative to the ambient CO2 treatment. At the 29/21 degrees C optimal growth temperature, grain yield increased on average c. 50% wi th enriched CO2. In contrast, at the higher growth temperature (37/29 degrees C), grain yield was almost zero, presumably due, in part, to t emperature-induced infertility (i.e. the percentage of filled spikelet s was < 1%), Among cultivars, IAC 165, a tropical japonica from Brazil , showed the largest relative increase in both biomass and grain yield , While the range of responses to increased CO2 and/or temperature wer e quite large (e.g. 10-250%) and may not be applicable to field condit ions, data indicate that lines are available which could maximize prod uctivity as CO2 concentration increases. Additional work, however, wou ld be needed to identify cultivars which would maintain maximum yields in a high CO2, high temperature environment.