Plasticidade e aclimatação fotossintética de espécies arbóreas tropicais

• Autor(a) principal: Ribas, Rogério Ferreira
• Data de Publicação: 2006
• Tipo de documento: Tese
• Idioma: por
• Título da fonte: LOCUS Repositório Institucional da UFV
• Texto Completo: http://locus.ufv.br/handle/123456789/975
• topic: Fotossíntese; Fluorescência; Fotoinibição; Árvores tropicais; Anatomia quantitativa; Photosynthesis; Fluorescence; Photoinhibition; Tropical trees; Quantitative anatomy; CNPQ::CIENCIAS BIOLOGICAS::BOTANICA::FISIOLOGIA VEGETAL

The aim of this work was the study of the correlation between the degree of photosynthetic plasticity/acclimation and the sucessional stage of tropical tree species. In order to assess this phenomena two different evaluation approaches were used: (i) the physiological and anatomical alterations in young plants of eight tree species cultivated under natural conditions of understory, and gap and (ii) the effects of the increment on the solar radiation, due to the simulated opening of gaps, on the physiological characteristics of the plants cultivated under understory conditions. The effect of different light regimes was also evaluated. On either case the parameters analyzed were the daily courses of the gaseous exchange and the chlorophyll fluorescence, the chloroplastidic pigments content and quantitative anatomical characteristics. The research was made in the Station of Research, Training and Environmental Education Mata do Paraiso (EPTEA Mata do Paraiso) and the studied species were: Centrolobium tomentosum, Genipa americana, Nectandra rigida, Ocotea odorifera, Platymiscium pubescens, Siparuna guianensis, Sorocea bonplandii and Spondias dulcis. In general, most of these species were able to adjust to the light regime that they were exposed to. The reduction in the light density was followed by noticeable decreased in the maximum photosynthetic capacity (Amax), in the saturation irradiance (I), in the apparent electron transport rate (ETR), in the non photochemical quenching coefficient (NPQ), in the relationships between chlorophyll a/b, total carotenoids/chlorophyll and in the thickness ratio of the limbo and the palisade parenchyma. The extension of those alterations varied from species to species, being less pronounced in those commonly found on the understory. In the gap, representatives of these species also exhibited, before dawn and during the duration of the light period, values of quantum photon yield (Fv/Fm) below 0.8 and the smallest values of effective quantum yield (F/Fm') and ETR during the period of maximum irradiance, indicating the on set of chronic photoinhibition and the lower photochemical performance under high light density. The study of the effect of simulated gaps on the physiological characteristics of the understory plants revealed that the photosynthetic rate was severely reduced in response to the sudden increment of the light density. Such reduction was accompanied by a substantial fall in the Fv/Fm ratio, which was in part due to an irreversible increase on F0, indicating the occurrence of oxidative damages on the light harvest complex and on the photosystem II reaction center. It was also observed that under prolonged subjection to high irradiance, the duration and the magnitude of the photoinhibition varied substantially among the species and in some cases the plants stayed chronically photoinhibited. However, in most cases, the photoinhibited plants recovered the initial rate of assimilation and/or exhibited significant increases in Amax followed by bigger Is and ETR. The most pronounced increments in Amax were observed in S. dulcis, followed by G. americana, N. rigida, S. guianensis, P. pubescens, C. tomentosum, S. bonplandii and O. odorifera. Overall, these results demonstrated a correlation between the photosynthetic acclimatization capacity of the species and their natural occurrence in the understoty and gap condition. Nonetheless, such finding tended to be more pronounced in the species from the gap rather than the understory condition.