Plasticidade do cafeeiro à luz: respostas morfofisiológicas em genótipos de Coffea arabica L

• Autor(a) principal: Silva, Mariela Mattos da
• Data de Publicação: 2013
• Tipo de documento: Tese
• Idioma: por
• Título da fonte: LOCUS Repositório Institucional da UFV
• Texto Completo: http://locus.ufv.br/handle/123456789/1001
• topic: Coffea arabica; Plasticidade fenotípica; Limitações; Coffea arabica; Phenotypic plasticity; Limitations; CNPQ::CIENCIAS BIOLOGICAS::BOTANICA::FISIOLOGIA VEGETAL

In this study, three genotypes of Coffea arabica L., subjected to contrasting light conditions (full sun and shade), were assessed to investigate the possible effects of shading on: (i) the characteristics of the photoprotective and antioxidative system, (ii) the costs of construction and maintenance of the plant tissues, (iii) the phenotypic plasticity and its relationship with shade tolerance, and (iv) to evaluate the key limiting processes to photosynthesis. To this goal, plants were grown either under shade for a year (10 % of solar radiation) or full sun light, and evaluated after the appearance of the eighth pair of plagiotropic branches. In the first section, we tested the hypothesis that modern cultivars (Catuaí) display higher plasticity associated with antioxidative and photoprotective system than older cultivars (Typica), presumably with less tolerance to high irradiances. The results showed that, overall, the photosynthetic variables evaluated responded little, if any, to the treatments, although full sun plants tend to have higher values than those in the shade (except the efficiency of excitation energy capture by open photosystem II reaction centers, Fv'/Fm', and the photoinhibitory quenching coefficient, qI). Increases in antioxidant activity were associated with increases in enzymatic and non-enzymatic defenses (carotenoids and phenols). However, these mechanisms did not prevent the occurrence of oxidative damage in Typica and Bourbon plants grown under full sun, as judged from the increases in malondialdehyde content. Particularly, Typica presented the lowest concentrations of zeaxanthin (Zea) in full sun pants, with increases in qI in response to high light availability in sun plants. Given that Zea seems to have an important role in processes involved in qI formation, the observed increases in Typica may be a result of reductions in concentrations of Zea in full sun plants, and could explain the susceptibility of this cultivar to photoinhibition. Furthermore, the highest levels of Zea in Catuaí and Bourbon may have contributed to the reduction of qI and increased protection against photodamages. Higher costs of construction and maintenance (CM) were found in sun-expanded leaves, mainly in Typica plants. It is suggested that the adjustment of the Catuaí plants to high irradiances may be related to more efficient antioxidative and photoprotective mechanisms, and greater photosynthetic plasticity. Moreover, although having a higher phenotypic plasticity associated with antioxidant system, Typica plants showed higher risks of suffering from photodamage and photoinhibition at high light intensities. In the second section, it was analyzed the contributions of the main factors that govern the changes of photosynthesis throughout the day in C. arabica, and the contribution of intraspecific variation in leaf hydraulic capacity and its potential influence on the differences observed between modern genotypes compared to those that retained characteristics associated with tolerance to shade in the field. The results showed that, although the photosynthetic rates (A) throughout the day have followed the same pattern as that of stomatal conductance (gs) and mesophyll conductance (gm), the diurnal adjustment of stomatal aperture was the main limiting factor to photosynthesis in coffee in full sun plants (more than 40 % of the total limitation). Stomatal limitations were, thus, of great importance to explain the low photosynthetic rates in coffee, followed by mesophilic and biochemical limitations, which tended to have similar magnitudes (and similar importance). Strong correlations were observed between gs, vapor pressure deficit and particularly, leaf hydraulic conductance (KL), indicating that KL might act as the primary factor in the reduction of gs. Notably, although Typica plants display a photosynthetic capacity similar to that of other cultivars, a major constraint on the maximization of photosynthetic rates may be the result of a less robust hydraulic architecture, which might at least partially explain the low productivity of this cultivar when grown in full sun.