The Response of Oxygen and Carbon Dioxide Exchanges and Root Activity to Short Term Water Stress in Soybean

The gross and net O₂ evolution together with O₂ uptake, CO₂assimilation, transpiration, shoot dark respiration, root respirationand ion uptake of a soybean plant were studied during 19 d whichincluded two periods of water stress. O₂ uptake was measuredusing ¹⁸O₂ as a tracer. Short term water stress induced immediateand lasting effects: (1) reduction of light interception bywilting, (2) limitation of the total reducing equivalent producedby the electron transport chain, (3) decrease of stomatal conductancereducing both losses of water and the entry of CO₂ for assimilation,(4) relative stimulation of O₂ uptake. The ratio of O₂ uptaketo CO₂ assimilation changed from 1.0 before stress to 1.4 forseveral days after. Root respiration was less affected by thestress than ion uptake and shoot gas exchanges. Key words: Photosynthesis, Photorespiration, Transpiration, Shoot and root respiration, Ion uptake, Water stress, Glycine max. L.