Key leaf traits indicative of photosynthetic plasticity in tropical tree species

The main achievement of this work was an attempt to determine the best association between five tropical species and light environments, based on the physiological and morphological characters related to photosynthesis. Information about light tolerance and photosynthetic plasticity of indigenous tropical tree species is still limited, particularly information of first years of plants' development. In this study, we evaluated the adjustments in response to different light environments of 25 leaf traits most commonly assessed in studies on light acclimation of photosynthesis in current literature. This evaluation was used to investigate the photosynthetic plasticity on young plants of five tropical tree species belonged to different successional groups. All the species are commonly used in forest restoration programs in Brazil. Plants were grown for 6 months under different light conditions simulating environments that could exist due to variation in naturally occurring canopy openings of secondary tropical forests. The level of adjustment on leaf traits to environmental conditions was calculated via a plasticity index. The relation between leaf trait adjustments and species photosynthetic plasticity was investigated by multivariate Biplot analyses. We selected the seven most explicative leaf traits of the photosynthetic plasticity of the studied species in response to different light environments: dark respiration rate (R (d)), Rubisco carboxylation capacity (V (cmax)), total chlorophyll content (ChlT), contribution of spongy parenchyma (%SP), contribution of leaf collenchyma tissue (%C), chlorophyll parenchyma thickness (PP/SP) and specific leaf area (SLA). Based on the selected traits, we identified the traits most related to high plasticity (V (cmax), PP/SP, %SP, %C and SLA) and low plasticity (V (cmax), R (d) and ChlT) and grouped species into three different patterns of photosynthetic plasticity. Our plasticity grouping was not correlated with species successional classification, indicating the importance of including physiological features related to light tolerance in species successional classifications. This work provides complementing information to traditional species successional groupings and to our current ability to select species for enrichment planting on restoration efforts.