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Stomatal and photochemical limitations of photosynthesis in Coffea spp. plants subjected to elevated temperatures
Temperature increase assumes a prominent role among expected climate change due to its significant impact on plant metabolism. As regards the C-assimilation pathway, high temperature can have impacts at both stomatal and non-stomatal levels, mainly linked to stomatal closure and photochemical and biochemical limitations. However, in general plants have some ability to trigger acclimation mechanisms to cope with stressful conditions, especially if those limitations are imposed in a gradual manner along seasonal change. This study aims at evaluating changes at stomatal and photochemical levels in Coffea arabica and C. canephora under mild temperature (spring) and high temperature (summer) exposure. Potted plants were, maintained in a greenhouse, watered to field capacity and subject to the natural variations of light, temperature and relative humidity. Exposure to summer conditions decreased photosynthetic rates (A), stomatal conductance (gs) and stomatal density (SD) and increased intrinsic water use efficiency (iWUE) in C. arabica when compared to spring values, while C. canephora plants maintained similar values in both seasons. However, during spring C. canephora presented lower A and gs than C. arabica. Since photosynthetic capacity (Amax), photosynthetic index (PI) and membrane permeability were similar between genotypes and seasons, while maximum quantum yield (Fv/Fm) and photosynthetic pigments were not affected in C. arabica in summer, we conclude that under high temperature conditions, stomatal closure imposes the major limitation in C. arabica photosynthesis in summer. Finally, both coffee genotypes were able to avoid damage to photochemistry pathway under supra-optimal temperatures.
CP17044 Accepted 09 January 2018
© CSIRO 2018