Abstract
The xylem is a complex system that includes a network of dead conduits ensuring long-distance water transport in plants. Under ongoing climate changes, xylem embolism is a major and recurrent cause of drought-induced tree mortality. Non-structural carbohydrates (NSC) play key roles in plant responses to drought and frost stress, and several studies putatively suggest their involvement in the regulation of xylem water transport. However, a clear picture on the roles of NSCs in plant hydraulics has not been drawn to date. We summarize the current knowledge on the involvement of NSCs during embolism formation and subsequent hydraulic recovery. Under drought, sugars are generally accumulated in xylem parenchyma and in xylem sap. At drought-relief, xylem functionality is putatively restored in an osmotically driven process involving wood parenchyma, xylem sap and phloem compartments. By analyzing the published data on stem hydraulics and NSC contents under drought/frost stress and subsequent stress relief, we found that embolism build-up positively correlated to stem NSC depletion, and that the magnitude of post-stress hydraulic recovery positively correlated to consumption of soluble sugars. These findings suggest a close relationship between hydraulics and carbohydrate dynamics. We call for more experiments on hydraulic and NSC dynamics in controlled and field conditions.
Highlights
The maintenance of long-distance water transport is an essential requisite for the survival and competitive success of vascular land plants
By analyzing the published data on stem hydraulics and Non-structural carbohydrates (NSC) contents under drought/frost stress and subsequent stress relief, we found that embolism build-up positively correlated to stem NSC depletion, and that the magnitude of post-stress hydraulic recovery positively correlated to consumption of soluble sugars
In the light of the putative mechanisms of hydraulic regulation summarized in this review, we recognize the urgent need to design experiments in both controlled and field conditions that include the analysis of xylem sap, wood and bark NSC separately, and that in parallel quantify embolism during both drought and drought relief
Summary
The maintenance of long-distance water transport is an essential requisite for the survival and competitive success of vascular land plants. Under ongoing climate changes apparently leading to increased intensity and frequency of drought events [2], hydraulic failure, i.e., the loss of substantial hydraulic function that induces plant desiccation, is a major and recurrent cause of tree mortality and forest decline worldwide [3]. The main goals of this review are (i) to provide a view on the state-of-the-art on the role of NSCs in the maintenance of water transport in woody plants under drought and recovery; and (ii) to identify possible relationships between tree hydraulic and NSC dynamics
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