Location: Crops Pathology and Genetics ResearchTitle: In-vivo pressure gradient heterogeneity increases flow contribution of small diameter vessels in grapevine
|BOUDA, MARTIN - Yale University|
|WINDT, CAREL - Forschungszentrum Juelich Gmbh|
|BRODERSEN, CRAIG - Yale University|
Submitted to: Nature Communications
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/19/2019
Publication Date: 12/10/2019
Citation: Bouda, M., Windt, C., McElrone, A.J., Brodersen, C. 2019. In-vivo pressure gradient heterogeneity increases flow contribution of small diameter vessels in grapevine. Nature Communications. 10. Article 5645. https://doi.org/10.1038/s41467-019-13673-6.
Technical Abstract: Plant leaves exchange water molecules for carbon dioxide at a ratio of approximately 400:1 to drive photosynthesis. Most xylem sap, a constant stream of water from soil to leaf, replaces lost water to prevent desiccation. Theory predicts that flow rates within xylem conduits are proportional to the radius raised to the fourth power, but we currently lack empirical flow measurements of individual xylem conduits in vivo to substantiate this framework. Here, we confront theoretical flow predictions with in vivo flow observations using magnetic resonance imaging (MRI) and a vessel network reconstructed from microCT imagery from the same sample. We demonstrate the unexpected presence of transverse pressure gradients locally exceeding the dominant axial gradient by an order of magnitude. Transverse gradients arise from significant heterogeneity in xylem network resistances that reflect both individual conduit properties and emergent properties of the network. Our data show a significant deviation of flow away from the widest vessels, which are historically believed to carry most of the water to the canopy. We show that the relative contribution of individual vessels to axial flow cannot be estimated without an understanding of their place in the overall network, necessitating a significant amendment to the Cohesion-Tension Theory. Both theoretical insights into xylem construction strategies or optimal vessel characteristics and empirical methods for measuring xylem water potential and conductance rely on an assumption of homogeneity of the medium. Our work calls for a revision to this working model of xylem as a porous medium to account for this heterogeneity.