Inga marginata and Inga subnuda are evergreen N-fixing tree species that are frequently found in the initial stages of forest regeneration. I. marginata has a wide geographic distribution, encompassing the Brazilian Atlantic Rainforest and dry forests of central Brazil, whereas I. subnuda is endemic to the Brazilian Atlantic Rainforest. We conducted this study to compare the physiological, growth, and biomass allocation responses of I. marginata and I. subnuda to contrasting light environments. Considering that I. marginata and I. subnuda have a similar position in the forest succession and different geographic distributions, we tested a hypothesis that these two congeneric species have similar photosynthetic and growth responses to light availability but different biomass allocation. The plants were grown under three light conditions (36, 15, and 6 mol photons m⁻² day⁻¹) for 105 days. Growth, biomass allocation, light–response curves, and leaf pigments were compared among the light conditions and between species by using two-way ANOVA. Our hypothesis was partially supported because the two species had similar photosynthetic responses to changes in light availability, but differences in growth and biomass allocation. The higher relative growth rate in mass of I. subnuda is associated with its higher allocation of biomass to light capture, as shown by the higher values of leaf mass fraction (LMF) and leaf area ratio (LAR). Conversely, the higher values of root mass fraction for I. marginata were in contrast to the higher values of LMF, LAR, and specific leaf area for I. subnuda; this indicates that I. marginata should be better adapted to environments where water could be a limiting factor, which is consistent with its wide geographic distribution.
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