The larger decrease in
Fv/Fm under aerobic condition than flooded condition was thought to be caused by the photosynthetic
depletion derived from stomatal closure. The decrease of Fv/Fm occurred concomitantly with the increase
of non-photochemical quenching (NPQ). Enhanced photoinhibition and NPQ might oxidize the redox state
of the plastoquinone (PQ) pool under the aerobic condition to the same level as that under the flooded
condition. The genotypic variation of the Fv/Fm and energy partitioning were affected little by the mild soil
water deficiency of the aerobic condition. The genotypic variation of the midday Fv/Fm was dependent on
the decreasing rate of Fv/Fm against an increase in midday light intensity. Some genotypes that showed
more severe midday photoinhibition tended to have a lower rate of reduction of the shoot dry weight
under the aerobic condition.