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Keywords:

  • Leaf productivity;
  • leaf longevity;
  • soybean;
  • Glycine max;
  • leaf and canopy photosynthesis

Summary

To understand the structure and dynamics of the leaf population composing a canopy, a life table analysis using rates of leaf emergence, mortality and dry matter production was applied to the foliage of soybean plants grown at three densities and sown at three times.

The mean leaf longevity differed greatly depending on the time of sowing, but in the early sown plants little difference was found among the leaves of lower and middle layers of the canopy in spite of the wide difference in the irradiance of the layers.

The rate of net photosynthesis of upper leaves in full daylight tended to decline gradually owing to senescence in leaves older than 20 d. That of lower-layer leaves, in very dark conditions, decreased very rapidly owing to both shading and senescence. Analyses of the survivorship curves and the time trends of net photosynthetic rates showed that lower leaves in densely planted populations survived for quite a long time after they had lost the ability to produce additional dry matter.

The rate of canopy net photosynthesis tended to follow a saturation curve with the increase in the leaf area index of whole canopy. There was no optimum leaf area index that maximized canopy photosynthetic rate.