In vivo pressure gradient heterogeneity increases flow contribution of small diameter vessels in grapevine

Abstract

Leaves lose approximately 400 H 2 O molecules for every 1 CO 2 gained during photosynthesis. Most long-distance water transport in plants, or xylem sap flow, serves to replace this water to prevent desiccation. Theory predicts that the largest vessels contribute disproportionately to overall sap flow because flow in pipe-like systems scales with the fourth power of radius. Here, we confront these theoretical flow predictions for a vessel network reconstructed from X-ray μCT imagery with in vivo flow MRI observations from the same sample of a first-year grapevine stem. Theoretical flow rate predictions based on vessel diameters are not supported. The heterogeneity of the vessel network gives rise to transverse pressure gradients that redirect flow from wide to narrow vessels, reducing the contribution of wide vessels to sap flow by 15% of the total. Our results call for an update of the current working model of the xylem to account for its heterogeneity.

Drought-Induced Xylem Embolism Limits the Recovery of Leaf Gas Exchange in Scots Pine

“…For this reason, nonintrusive methods provide a welcoming alternative to visualize the hydraulic status of xylem conduits in vivo. Examples include the application of magnetic resonance imaging (Holbrook et al, 2001;Bouda et al, 2019) and Xray microtomography (Brodersen et al, 2010;Choat et al, 2015Choat et al, , 2016Choat et al, , 2019Nardini et al, 2017). Application of these high-tech methods has become increasingly popular in recent years, providing novel insights into the ability of plants to recover embolized conduits following release from drought.…”

Persistent decay of fresh xylem hydraulic conductivity varies with pressure gradient and marks plant responses to injury

“…In all these modelling applications, special care should be taken in defining K x , as assuming it a constant value could represent an oversimplification since K x might vary in response to biotic and abiotic stresses (see also Millar et al, 2017), as well as in response to pressure gradients and their history. The highlighted linkages between the macroscopic and microscopic behaviours point to the necessity to better relate the bulk hydraulic parameterization to the xylem network topology accounting explicitly for pressure‐dependence flow paths and thus for a redundant network during normal operating conditions (Bouda, Windt, McElrone, & Brodersen, 2019; Manzoni et al, 2013; Mrad, Domec, Huang, Lens, & Katul, 2018).…”

Grafted semiconducting polymer amphiphiles for multimodal optical imaging and combination phototherapy

“…Although optical imaging has shown great potential in biomedical applications, traditional imaging modalities such as magnetic resonance imaging (MRI) and X-ray computed tomography (CT) imaging have their own advantages and are irreplaceable in clinical diagnosis. 95 Thus, multimodal imaging which combines optical and traditional imaging modalities may provide better diagnostic efficacy than any single modality.…”