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Keywords:

  • aerenchyma;
  • flooding;
  • Oryza sativa;
  • oxygen transport;
  • root aeration;
  • submergence;
  • underwater photosynthesis

Summary

  • • 
    Complete submergence of plants prevents direct O2 and CO2 exchange with air. Underwater photosynthesis can result in marked diurnal changes in O2 supply to submerged plants. Dynamics in pO2 had not been measured directly for submerged rice (Oryza sativa), but in an earlier study, radial O2 loss from roots showed an initial peak following shoot illumination.
  • • 
    O2 dynamics in shoots and roots of submerged rice were monitored during light and dark periods, using O2 microelectrodes. Tissue sugar concentrations were also measured.
  • • 
    On illumination of shoots of submerged rice, pO2 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 pO2 was one order of magnitude higher than in darkness, enhancing also pO2 in roots.
  • • 
    The initial peak in pO2 following illumination of submerged rice was likely to result from high initial rates of net photosynthesis, fuelled by CO2 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 pO2 after longer periods of submergence.