Some Photosynthetic Characteristics of Tropical Timber Trees as Affected by the Light Regime During Growth

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Abstract
The stomatal conductance and rate of photosynthesis of tropical tree seedlings are reported (Terminalia ivorensis, T. superba, Triplochiton scleroxylon and Khaya senegalensis). The seedlings were grown in various light regimes, defined by the photon flux density and red: far-red ratio. Mesophyll conductance and apparent quantum efficiency were calculated. The maximum rates of photosynthesis on an area or weight basis depended on the photon flux density during growth, being increased by growth at high photon flux density except in the shade tolerant seedlings of K. senegalensis. The stomatal conductance was also highest in leaves which had been grown at high photon flux density. Using plants which had been grown at low photon flux density and contrasting red: far-red ratio, it was found that the highest rates of photosynthesis were attained when the red: far-red ratio was low. The results are discussed in relation to what is known of the natural light climate, and evaluated in relation to the carbon balance of seedlings.