ATMOSPHERIC CO2 AND TEMPERATURE EFFECTS ON DEVELOPMENT AND GROWTH OF RICE

Atmospheric CO2 is expected to exceed 600 mul-1 by the 21st century an d is predicted to increase global mean temperature by 0-8-degrees-C. B ecause CO2 and temperature are expected to increase together, we condu cted controlled-environment chamber research to assess the effects of two CO2 concentrations (330 and 660 mul l-1) and three temperature reg imes (29/21, 33/25, 37/29-degrees-C, day/night temperature) on three l owland (IR28, IR36, IR64) and three upland (ITA186, Moroberekan, Salum pikit) rice cultivars. At 330 mul l-1 CO2, most cultivars grew best at 33/25-degrees-C. Doubling CO2 increased plant height by 17% at 29/21- degrees-C and by 7% at 33/25-degrees-C, but reduced plant height by 3% at 37/29-degrees-C. Increasing temperature from 29/21 to 37/29-degree s-C reduced tiller number by 10% but doubling CO2 more than offset thi s effect so that tiller number was 66% greater in the high CO2, high t emperature treatment than in the low CO2, low temperature treatment at 45 days after sowing. In the lowland cultivars the combination of hig her CO2 and higher temperature doubly shortened the vegetative and rep roductive phase, while at 29/21-degrees-C, increased CO2 delayed onset of the reproductive phase. At 29/21-degrees-C, doubling CO2 increased time to flowering by 6% but at 37/29-degrees-C, doubling CO2 decrease d time to flowering by 6%. Flowering of ITA186 was not affected by CO2 level. Doubling CO2 increased total dry weight at flowering by 22%. T otal dry weight was inversely related to high temperature for the lowl and cultivars. Although controlled-environment experiments have their drawbacks, the present data indicate varietal differences in responses to CO2 and temperature and a significant interactive effects of CO2 a nd temperature on development of lowland rices. These differences may provide options to minimise adverse effects of future climate changes.