Photosynthesis and water relations of well-watered orange plants as affected by winter and summer conditions |
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Authors: | RV Ribeiro EC Machado MG Santos RF Oliveira |
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Institution: | (1) Section of Plant Physiology, Center for Research and Development in Ecophysiology and Biophysics, Agronomic Institute, P.O. Box 28, 13012-970 Campinas/SP, Brazil;(2) Department of Botany, Federal University of Pernambuco, 50670-901 Recife/PE, Brazil;(3) Department of Biological Sciences, “Luiz de Queiroz” College of Agriculture, University of Sao Paulo, P.O. Box 9, 13418-900 Piracicaba/SP, Brazil |
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Abstract: | The aim of this study was to evaluate how the summer and winter conditions affect the photosynthesis and water relations of
well-watered orange trees, considering the diurnal changes in leaf gas exchange, chlorophyll (Chl) fluorescence, and leaf
water potential (Ψ) of potted-plants growing in a subtropical climate. The diurnal pattern of photosynthesis in young citrus
trees was not significantly affected by the environmental changes when compared the summer and winter seasons. However, citrus
plants showed higher photosynthetic performance in summer, when plants fixed 2.9 times more CO2 during the diurnal period than in the winter season. Curiously, the winter conditions were more favorable to photosynthesis
of citrus plants, when considering the air temperature (< 29 °C), leaf-to-air vapor pressure difference (< 2.4 kPa) and photon
flux density (maximum values near light saturation) during the diurnal period. Therefore, low night temperature was the main
environmental element changing the photosynthetic performance and water relations of well-watered plants during winter. Lower
whole-plant hydraulic conductance, lower shoot hydration and lower stomatal conductance were noticed during winter when compared
to the summer season. In winter, higher ratio between the apparent electron transport rate and leaf CO2 assimilation was verified in afternoon, indicating reduction in electron use efficiency by photosynthesis. The high radiation
loading in the summer season did not impair the citrus photochemistry, being photoprotective mechanisms active. Such mechanisms
were related to increases in the heat dissipation of excessive light energy at the PSII level and to other metabolic processes
consuming electrons, which impede the citrus photoinhibition under high light conditions. |
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Keywords: | Additional" target="_blank">Additional Citrus sinensis chlorophyll fluorescence ecophysiology gas exchange seasonality |
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