As respostas ecofisiológicas em função da luz explicam a distribuição de Hymenaea courbaril L. (Fabaceae) em áreas de formações florestais e savânicas?

Abstract

Seedlings in natural environments are exposed to a wide range of light conditions. Excess light can cause photoinhibition, while reduced light availability can also lead to developmental issues in the early stages of plant growth. Understanding the morphophysiological responses of native plants to these conditions is crucial for improving their management. Hymenaea courbaril L. belongs to the Fabaceae family and is found in nearly all Brazilian biomes. To assess the morphophysiological capabilities of this species, 75 seeds of H. courbaril were sown in pots in a nursery. After germination and expansion of the cotyledons, 15 plants were selected for three treatments (100% irradiance in full sun, 7% irradiance in partial shade, and 1% irradiance in dense shade). Six plants were removed from the pots, and initial growth measurements (height, stem diameter, root length) and dry biomass determination were conducted. The seedlings remained under experimental conditions for 103 days. Measurements of potential, effective, and electron transport quantum yields were taken to assess potential photoinhibition. Gas exchange measurements (CO2 assimilation, stomatal conductance, and transpiration) and Falker Chlorophyll Index measurements were also conducted on the metaphylls and eophylls. After 103 days of the experiment, ten plants per treatment were removed from the pots for leaf area measurement, growth data, and dry biomass measurement. Using these data, organ mass ratios, specific leaf area, leaf area ratios between metaphylls and eophylls, and relative growth rate were calculated. Results showed dynamic photoinhibition in H. courbaril seedlings under 100% irradiance, without affecting their photosynthetic capacity. Shaded plants invested more resources in leaves, whereas those under full sun invested more in roots. All plants survived, but the relative growth rate of the most shaded plants was close to zero, while plants under higher light intensity showed a higher growth rate. Eophylls displayed characteristics that may aid plant survival in shade. The study demonstrated significant morphophysiological plasticity in Hymenaea courbaril, which exhibited complete survival under all conditions and was not negatively affected by high light irradiance.