A COMPARISON OF LIGHT QUALITY AND QUANTITY EFFECTS ON THE GROWTH AND STEADY-STATE AND DYNAMIC PHOTOSYNTHETIC CHARACTERISTICS OF 3 TROPICAL TREE SPECIES

1. The role of light quality and quantity on steady-state photosynthetic characteristics, efficiency of lightfleck utilization (LFUE) and growth was evaluated in seedlings of tropical rain-forest trees. 2. The pioneer species, Cecropia obtusifolia and Heliocarpus appendiculatus, and the shade tolerant species, Rheedia edulis, were grown in a greenhouse under contrasting red/far-red (R/FR) ratios characteristic of the open and the shaded forest understorey but with the same low photosynthetically active radiation (PAR). Additionally plants were grown in a high PAR environment with a R/FR characteristic of the open. 3. The pioneer species responded strongly to R/FR in terms of greater height growth and a shift in allocation to stem growth over leaf growth in low R/FR (simulated shade) as compared to high R/FR (open). Light quality, however, had no significant effect on steady-state photosynthetic characteristics or LFUE for any species. 4. Increased light quantity, by contrast, caused photosynthetic acclimation leading to higher photosynthetic capacities. The pioneer species showed a larger capacity for photosynthetic acclimation to light environment than the shade species. LFUE was also affected by light quantity, with the low-light grown plants showing higher LFUE than the high-light grown plants. 5. Results provide evidence that light quality does not play an important role in modulating steady-state and dynamic photosynthetic characteristics during acclimation to shade, even in species that exhibit morphogenetic responses to light quality.