SINGLE LEAF PHOTOSYNTHESIS OF RICE PLANTS UNDER FIELD CONDITIONS .5. LONG-TERM VARIATIONS IN PHOTOSYNTHESIS OF UPPER LEAVES

The patterns of variation with time on single-leaf photosynthesis (CER) varied among leaves according to the positions on the stem. In the second and the third leaves, CER under saturation light intensity was at the maximum at the full expansion, decreasing with time thereafter. CER of the flag leaf was rather low at the full expansion but increased rapidly attaining the double of the initial value after two weeks. After that, it decreased as in leaves at other positions. The CER increase in the flag leaf at the early stage was brought about by an increase primarily in stomatal conductance (gs) and secondarily in mesophyll photosynthetic activity. The CER decrease observed in all leaves at later stages was resulted from a decrease primarily in mesophyll photosynthetic activity and secondarily in gs. In the second and the third leaves, the initial slope of light-CER curve was at the maximum at the full expansion decreasing with time thereafter. In the case of the flag leaf, the slope was small at the full expansion, increasing considerably at first, but decreased later. The degrees of both increase and decrease were much larger than that of the slope variation in the second and the third leaves. © 1990, CROP SCIENCE SOCIETY OF JAPAN. All rights reserved.