Oxygen dynamics in submerged rice ( Oryza sativa )

Summary•  Complete submergence of plants prevents direct O 2 and CO 2 exchange with air. Underwater photosynthesis can result in marked diurnal changes in O 2 supply to submerged plants. Dynamics in pO 2 had not been measured directly for submerged rice ( Oryza sativa ), but in an earlier study, radial O 2 loss from roots showed an initial peak following shoot illumination. •  O 2 dynamics in shoots and roots of submerged rice were monitored during light and dark periods, using O 2 microelectrodes. Tissue sugar concentrations were also measured. •  On illumination of shoots of submerged rice, pO 2 increased rapidly and then declined slightly to a new quasi‐steady state. An initial peak was evident first in the shoots and then in the roots, and was still observed when 20 mol m −3 glucose was added to the medium to ensure substrate supply in roots. At the new quasi‐steady state following illumination, sheath pO 2 was one order of magnitude higher than in darkness, enhancing also pO 2 in roots. •  The initial peak in pO 2 following illumination of submerged rice was likely to result from high initial rates of net photosynthesis, fuelled by CO 2 accumulated during the dark period. Nevertheless, since sugars decline with time in submerged rice, substrate limitation of respiration could also contribute to morning peaks in pO 2 after longer periods of submergence.