Diurnal and developmental changes in energy allocation of absorbed light at psii in field-grown rice

The allocation of absorbed light energy in PSII to electron transport and heat dissipation processes in rice grown under waterlogged conditions was estimated with the lake model of energy transfer. With regard to diurnal changes in energy allocation, the peak of the energy flux to electron transport, J _PSII, occurred in the morning and the peak of the energy flux to heat dissipation associated with non-photochemical quenching of Chl fluorescence, J_NPQ, occurred in the afternoon. With regard to seasonal changes in energy allocation, J_PSII in the rapidly growing phase was greater than that in the ripening phase, even though the leaves of rice receive less light in the growing phase than in the ripening period in Japan. This seasonal decrease in J_PSII was accompanied by an increase in J_NPQ. One of the reasons for the lower J_PSII in the ripening phase might be a more sever afternoon suppression of J_PSII. To estimate energy dissipation due to photoinhibition of PSII, J_NPQ was divided into J_fast, which is associated with fast-recovering NPQ mainly due to qE, and J_slow, which is mainly due to photoinhibition. The integrated daily energy loss by photoinhibiton was calculated to be about 3-8% of light energy absorption in PSII. Strategies for the utilization of light energy adopted by rice are discussed. For example, very efficient photosynthesis under non-saturating light in the rapidly growing phase is proposed.