DEVELOPMENTAL RESPONSES OF RICE TO PHOTOPERIOD AND CARBON-DIOXIDE CONCENTRATION

The documented increase in the carbon dioxide concentration of the Earth's atmosphere has stimulated interest in the effects of CO2 on plants and in particular the future prospects for the world's food supplies. While rice is a major food crop, relatively little is known about the effects of CO2 concentration on the timing of physiological growth stages and total growth duration, which are important aspects of a rice cultivar's adaptability to the environment of a particular geographic region. The objective of this study was to determine the developmental responses of a modern, improved rice cultivar (Oryza sativa, cultivar 'IR-30') to a range of CO2 concentrations under two contrasting photoperiods. Rice plants were grown season-long in an outdoor, naturally lit, computer-controlled environment, plant growth chambers in CO2, concentrations of 160, 250, (subambient) 330 (ambient), 500, 660 and 900 (superambient) μmol CO2 mol-1 air. The entire experiment was conducted twice during 1987. The first or early planted rice (EPR) experiment was conducted with photoperiod extension lights during the vegetative phase of development, while the second or late-planted rice (LPR) experiment was conducted using only naturally occurring photoperiod. In both experiments, mainstem leaf developmental rates were greater during vegetative rather than reproductive growth stages and leaf appearance rates increased with CO2 treatment during vegetative development. In the LPR experiment, panicle initiation and boot stage occurred earlier and total growth duration was shortened for rice plants in the superambient compared with ambient and subambient CO2 treatments. This acceleration of plant development with increasing CO2 treatment was associated with a CO2-induced decrease in the number of mainstem leaves formed during the vegetative phase of growth. The reduced developmental response of rice plants to CO2 in the EPR compared with the LPR experiment was attributed to the artificially extended photoperiod during the EPR experiment forcing a delay in the onset of reproductive development particularly in the superambient treatments. The CO2-induced acceleration of development and shortening of total growth duration should become a topic of interest for rice agronomists and breeders involved with selecting rice cultivars and agronomic practices for a particular geographic region in view of the continued increases in global atmospheric CO2 concentration. © 1990.