Growth, photosynthetic responses and acclimaton of tree species to different light environments

• Autor(a) principal: Nina Junior, Adamir da Rocha
• Data de Publicação: 2019
• Tipo de documento: Tese
• Idioma: eng
• Título da fonte: Repositório Institucional do INPA
• Texto Completo: https://repositorio.inpa.gov.br/handle/1/5001; http://lattes.cnpq.br/8816936810059985
• topic: Espécies de árvore; Fotossíntese; Fotoinibição

Light is a fundamental resource for energy flow in biological systems and is highly determinant for plant life. The great variability in the natural environment requires that plants, especially trees, exhibit a great ability to adjust metabolism to spatial and seasonal variations in the availability of this resource, aiming not only to maximize the capture and use of light, but also the development of efficient mechanisms in the dissipation of excess light energy to avoid photoinhibitory damages to photosynthetic apparatus. In this context, the objective of this study was to evaluate the photosynthetic plasticity and light acclimation capacity of six Amazonian tree species (Hymenea courbaril, Carapa guianensis, Hevea brasiliensis, Tabebuia serratifolia, Bellucia grossularioides and Ochroma pyramidale) divided into different successional groups (two late successionals, two mid-successional and two pioneers, respectively) in response to different light conditions (full sunlight [FS - 100 % of solar radiation, which simulates a clearing area], moderate shade [MS - provide by shade cloths reducing direct incident solar radiation] and deep shade [DS - provided by adult tree canopies, which simulate an understory light environment]).The photosynthetic circadian rhythm and NSC accumulation/turnover, relative growth and biomass accumulation rates, maximum photosynthesis and their limitations, leaf N partition, antioxidant system activity and transients of chlorophyll a fluorescence were evaluated in four individuals per species and per environment using multivariate analyzes. Regardless of the light regime, the limitations to daily photosynthetic course were preponderantly diffusive. The pioneer species and H. courbaril exhibited the highest photosynthetic rates and higher accumulation of biomass in FS. In DS, greater photosynthesis was observed for B. grossularioides, however, this did not reflect in a greater accumulation of biomass while in this environment. The morphological changes most correlated to acclimation were leaf area in DS and leaf gain in FS. The leaf nitrogen partition between photosynthetic and structural compounds was more determinant for photosynthesis than its own content, since the ability to modulate the N allocation is fundamental for increasing or decreasing photosynthesis as a consequence of changes in the light environment. There was higher N foliar investment in Rubisco by the pioneers in FS, which also showed higher photosynthetic rates, electron transport and carboxylation rate in this environment. Despite the smaller Vcmax in DS, the plants exhibited a higher activation state of Rubisco suggesting a better ability to take advantage of sunflecks, especially in late successional species. Regarding the antixodative system, the SOD activity was fundamental for the reduction of cell damage in FS, but this activity decreased n lower irradiances. Only the late successional C. guianensis exhibited photoinhibition in FS and the pioneer O. pyramidale did not survive on DS, suggesting that acclimation at high irradiance is less challenging than intense shading. The results suggest that growth while in a shaded environment is apparently determined more by factors related to starch accumulation and turnover than photosynthesis. Additionally, it can be concluded that the plasticity to regulate the leaf’s physiological and morphological adjustments and the capacity of acclimation in response to changes in light environment regime is not necessarily related to the successional group of species.