The Role of the Red/Far-Red Ratio in the Response of Tropical Tree Seedlings to Shade

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Abstract
The West African species Khaya senegalensis and Terminalia ivorensis were grown in a controlled environment, varying the photon flux density in the range 18–610 μmol m−2 s−1 and the red/far-red ratio over an appropriate range to simulate the shade of a tree canopy versus unattenuated daylight. The shade tolerant seedlings of Khaya were relatively insensitive to the red/far-red ratio. The light demanding Terminalia was considerably affected: when the ratio was low the specific leaf area was increased and the leaves produced were very much larger in area. Thus, the Leaf Area Ratio was enhanced and the plants displayed an increase in Relative Growth Rate.