Soluble carbohydrates metabolism sustains energetics and xylem hydraulic functionality upon relief from drought in Populus tremula x alba

The role of non-structural carbohydrates (NSC) in tissues of woody plants during drought stress reveals different, sometimes contrasting, scenarios. A reduction of NSC level probably denotes that plant is undergoing a carbon starvation and consequently exposed to dieback. On the contrary, when soluble carbohydrates content increases, their possible role as osmotic compounds protecting from drought effects and trigging recovery is suggested. Our study focused on depicting the relationship between energetic metabolism and response to drought. Poplar trees were subjected to a drought treatment followed by a period of recovery (re-watering). Physiological measurements (water potential, growth parameters, PLC) were monitored in combination with analysis of hexose phosphate sugars, ATP and key-enzymes activity involved in glycolysis and starch-sugar metabolism. Drought treatment resulted in an alteration of carbohydrate metabolism, drawing a picture in which stem tissues (bark and wood) and xylem sap, differently responded to water stress and recovery, activating sugar oxidative pathways and using alternative sources of NSC. These mechanisms represent a natural trade-off between plant growth and energetic requirements. Our results pointed out that drought triggers an alteration of the energetic status aimed at regulating stress response and subsequent recovery.