XVI International Botanical Congess

In Rio Piedras, Puerto Rico, saplings of mahogany hybrids (Swietenia mahagoni x macrophylla) were transplanted into low light (6% of full sun) medium light (33% of full sun), and high light (80% of full sun) environments. The saplings exhibited wide variation in height growth in all environments. Mean light-saturated photosynthetic rates were 5.2 micromol m-2 s-1 for low light, 5.6 for medium light and 6.6 for high light. Mean light compensation point was 8.5 micromol m-2 s-1 in low light, indicating that these hybrids are capable of positive photosynthesis under heavily shaded conditions. The variation in height growth appeared to be largely explained by the capacity to acquire nitrogen, for shorter plants had lower concentrations of foliar N than taller ones.