Gas Composition in the Internal Air Spaces of Deepwater Rice in Relation to Growth Induced by Submergence

Deepwater rice (Oryza sativa L.) responds to partial submergenceby rapid elongation of the internodes. The elongation of intactplants was measured during 7 days of submergence using angulartransducers. Growth rates began to increase within 3 to 4 hupon submergence and peaked after 3 days; they were higher inthe light than in the dark. The composition of the gas phasein the internodal air spaces was analyzed at different timesafter partial submergence. In the light, the O₂ concentrationsin internal gas compartments of intact plants dropped initially,but recovered largely within 90 min. During longer periods ofsubmergence, the internal O₂ concentration followed a diurnalpattern with O₂ levels being lower during the night than duringthe day. An O₂ gradient was found from the apical parts of theplant near the water surface to the basal parts of the shoot. Concentrations of CO₂ changed with a pattern inverse to thatof the O₂concentrations. The level of ethylene in the internodallacunae increased upon submergence and reached 1µl-liter^–1after 72 h. It was higher at the end of the dark period thanduring the day. The gas exchange of the submerged parts of the plant seems todepend mainly on mass flow of air from the atmosphere to theroot system. Mass flow through this pathway was determined atdifferent pressure gradients and was compared to the intakeof air into plants as established in earlier investigations.A significant decrease in gas flow resistance found during 7days of submergence may constitute a long-term adaptation toflooding. (Received August 30, 1988; Accepted October 25, 1988)