Roots Are Important Sources Of Carbohydrates During Flowering And Fruiting In 'valencia' Sweet Orange Trees With Varying Fruit Load

The influence of fruit loading on flowering and fruiting, CO2 assimilation, and non-structural carbohydrates (NSC) in citrus trees was evaluated in four-year-old 'Valencia' sweet orange grafted onto 'Rangpur' lime. One group of trees was completely de-fruited (DFT) on May 14 (autumn), whereas fruit were left on the remaining trees (FT). The seasonal variation in photosynthesis and stomatal conductance was unaffected by fruit loading, with the minimum diurnal-integrated CO2 assimilation (PNI) occurring in July (98.3mmolm-2day-1) and the maximum PNI occurring in November (199.5mmolm-2day-1). Fruit loading inhibited sprouting and flowering in the citrus trees, but this effect was not correlated with NSC in the leaves, branches, or roots. The DFT trees exhibited nearly four times as many reproductive structures as the FT trees, with a high remobilization of reserves. Our data showed that flowers are stronger sinks than fruit and that flowering is the most expensive phenological stage. 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