Limitações e potencialidades da fotossíntese no cafeeiro em função da irradiância

• Autor(a) principal: Martins, Samuel Cordeiro Vitor
• Data de Publicação: 2011
• Tipo de documento: Dissertação
• Idioma: por
• Título da fonte: LOCUS Repositório Institucional da UFV
• Texto Completo: http://locus.ufv.br/handle/123456789/4321
• topic: Aclimatação fotossintética; Níveis de luz; Coffea arabica; Photosynthetic acclimation; Light levels; Coffea arabica; CNPQ::CIENCIAS BIOLOGICAS::BOTANICA::FISIOLOGIA VEGETAL

The present study was carried out in order to analyse the contributions of hydraulic, diffusive (stomatal and mesophilic) and biochemical limitations to photosynthesis in coffee, the nitrogen partitioning within the photosynthetic machinery as well as its activation state in response to light. To this end, arabica coffee (Coffea arabica L.) plants were grown in pots during 12 months under two light availabilities (0 and 90% shading). Compared to sun plants, shade plants showed higher specific leaf area (63%), chlorophyll (76%), carotenoids (62%) and nitrogen (N) (15%) mass-based concentrations, as well as higher chlorophyll/N ratio (53%); in contrast, shade plants showed lower stomatal density (32%), stomatal index (20%), venation density (27%), stomatal (27%) and mesophyll (37%) conductance and N concentration on an area basis (30%). There were no differences in pigment concentrations (on an area basis) or in the chlorophyll a/b ratio between treatments. The N partitioning invested in Rubisco and electron transport chain components differed little between the phenotypes; however, higher N fraction was invested in structural components (13%) in shade plants compared to sun plants. There were no differences in mass-based gas exchange parameters except for the maximum carboxylation velocity calculated on a Cc basis, 24% higher in shade plants than in sun plants. In contrast, on an area basis, sun plants exhibited higher maximum carboxylation velocity (32%), maximum photosynthetic rate (45%) and electron transport rate (43%). Apparently, mesophyll conductance may be of equal or less importance than stomal conductance to explain the low photosynthetic rates in coffee, regardless of growth irradiance. It is suggested that the hydraulic architecture is the most limiting primary factor to photosynthesis in coffee plants. The results support the hypothesis that shade plants would take better advantage of sunflecks energy in relation to sun plants as a result of having higher activation states and lower induction losses, in addition to absence of photoinhibition in the shade leaves. The results help to explain, in part, the low photosynthetic nitrogen-use efficiency, as a consequence of high investment of N into non-photossynthetic components.