Relationship among night temperature, carbohydrate translocation and inhibition of grapevine leaf photosynthesis

Important processes such as plant respiration, repair of damaged photosystems and carbohydrate translocation occurs during night. The lack of photosyntate translocation can influence photosynthetic efficiency of the leaves in the subsequent day. Night temperature can play and important role influencing the carbohydrate translocation. The aim of the work was to test the effect of night temperature on the photosynthetic activity, and to assess the correlation between the accumulation of carbohydrates in the leaves due to the reduction of their overnight translocation. In two experiments, taking into account whole canopy and single leaf CO2 assimilation of Vitis vinifera, night temperature was correlated with the variation of CO2 assimilation between the afternoon and the subsequent morning. In a controlled experiment, such variation was correlated with the accumulation of carbohydrates in the leaves in particular for low night temperatures, suggesting a mechanism of end product feedback down regulation. High night temperature caused a poor export of carbohydrates from the leaf, but the increase of respiration caused a consistent decrease of the carbohydrate content in the leaf. In conclusion, night temperature plays a pivotal role in the carbon translocation during the night. Further to its impact on source-sink relationship, this mechanism can have an important impact on the CO2 assimilation of the plant during the day that can be negatively affected either by relatively low and relatively high temperature during the night.