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

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Abstract
The gross and net O2 evolution together with O2 uptake, CO2 assimilation, transpiration, shoot dark respiration, root respiration and ion uptake of a soybean plant were studied during 19 d which included two periods of water stress. O2 uptake was measured using 18O2 as a tracer. Short term water stress induced immediate and lasting effects: (1) reduction of light interception by wilting, (2) limitation of the total reducing equivalent produced by the electron transport chain, (3) decrease of stomatal conductance reducing both losses of water and the entry of CO2 for assimilation, (4) relative stimulation of O2 uptake. The ratio of O2 uptake to CO2 assimilation changed from 1.0 before stress to 1.4 for several days after. Root respiration was less affected by the stress than ion uptake and shoot gas exchanges.