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

The West African species Khaya senegalensis and Terminalia ivorensiswere grown in a controlled environment, varying the photon fluxdensity in the range 18–610 µmol m^–2 s^–1and the red/far-red ratio over an appropriate range to simulatethe shade of a tree canopy versus unattenuated daylight. Theshade tolerant seedlings of Khaya were relatively insensitiveto the red/far-red ratio. The light demanding Terminalia wasconsiderably affected: when the ratio was low the specific leafarea was increased and the leaves produced were very much largerin area. Thus, the Leaf Area Ratio was enhanced and the plantsdisplayed an increase in Relative Growth Rate. Khaya, Terminalia, tropical trees, shade, red/far-red ratio     

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

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