Aclimatação morfofisiológica da liana Rhynchosia melanocarpa Grear. ao aumento da intensidade de luz

Abstract

Phenotypic plasticity in response to variations in light availability is a key factor determining the establishment of seedlings in heterogeneous environments. This study evaluated the ecophysiological, photosynthetic, and growth responses of Rynchosia melanocarpa, a liana with a wide distribution among distinct kinds of vegetation physiognomies, such as Cerrado and Atlantic rain forest. The seedlings were subjected to three light conditions: full sunlight (FS), shade (SH), and transfer from shade to full sunlight (SH→FS). Chlorophyll a fluorescence, electron transport rate (ETR), Falker Chlorophyll Index, gas exchange, growth indices, and biomass allocation were assessed. Seedlings maintained under shade exhibited high maximum quantum yield of PSII (Fv/Fm ≈ 0.80), higher chlorophyll content, greater specific leaf area, and higher leaf area ratio, reflecting typical acclimation responses to low irradiance. Conversely, seedlings grown under full sunlight showed higher net CO₂ assimilation, increased electron transport rates, greater water-use efficiency, enhanced carboxylation efficiency, and greater biomass allocation to roots. The transfer from shade to full sunlight induced marked initial photoinhibition, evidenced by a sharp decline in Fv/Fm and effective quantum yield (ΔF/Fm'), accompanied by temporary leaf chlorosis. However, after 24 days, transferred plants showed partial recovery of photochemical efficiency, increased electron transport rate, and maintenance of high photosynthetic performance, indicating successful acclimation to the new light environment. These seedlings also exhibited relative growth rates comparable to those grown under full sunlight and greater height increment, suggesting preferential investment in vegetative growth during acclimation. Overall, the results demonstrate that R. melanocarpa possesses high physiological and morphological plasticity, combining conservative strategies under shade with high photosynthetic performance under full sunlight. This functional flexibility enables rapid recovery following abrupt changes in irradiance, highlighting the ecological potential of the species to establish across contrasting light environments, a characteristic commonly associated with pioneer or early secondary tropical tree species.