A numerical model of coupled phloem-xylem flows for dynamic long-distance transport in trees

Sellier Damien, Mammeri Youcef, Peynaud Emilie, Gomez-Gallego Mireia, Leuzinger Sebastian, Dumont Yves, Dickson Alan, Williams Nari. 2023. A numerical model of coupled phloem-xylem flows for dynamic long-distance transport in trees. In : 12th International Workshop on Sap Flow: Book of abstracts. ISHS. Rotorua : ISHS, Résumé, p. 42. International Workshop on Sap Flow. 12, Rotorua, Nouvelle-Zélande, 31 Octobre 2023/3 Novembre 2023.

Résumé : In trees, the vascular system is dual in structure and func)on. Sap flows upwards in the xylem to hydrate )ssues and refill reserves from transpira)on loss. In the leaves, some of the water recirculates into the phloem and sap, loaded with photoassimilates, flows downwards to supply )ssues with carbohydrates. Flow and counter-flow occur in physically separated but hydraulically connected pathways. Water exchanges take place all along them. Understanding the en)re system and its subprocesses is essen)al to precisely quan)fy the carbon-water fluxes at the soil-atmosphere interface. That understanding is also key to predict the func)onal limits of vascular transport and, when dysfunc)on occurs, how it will impact the vitality of plant communi)es subject to drought events and foliar pathogen outbreaks. Here we present an integrated, spa)ally explicit model of phloem-xylem transport. The model implements Münch's osmo-regulated pressure flow hypothesis for phloem transport and cohesion-tension for xylem transport. The changes of phloem pressure, carbohydrate concentra)on and xylem pressure over )me are governed by three coupled nonlinear par)al differen)al equa)ons. Sap flow velocity, volume flow and the amount of shrinkage and swelling are calculated as derived variables. The model uses a special-purpose numerical scheme and can simulate response to dynamic forcing such as the diurnal pamerns of phloem loading and transpira)on. Unlike in other models, transport equa)ons are solved for a surface and account for tangen)al movement of water and carbohydrates. Phloem and xylem are treated as elasto-porous media with distributed hydraulic and mechanical proper)es. We also present a semi-automated image processing method to calculate the theore)cal hydraulic conduc)vity of phloem and xylem )ssues based on their anatomy. Key hydraulic characteris)cs are given for the phloem of juvenile Pinus radiata D. Don.

Mots-clés libres : Phloem-xylem transport, Spatially explicit model, Nonlinear partial differential equation, Numerical modeling, Pinus radiata

Auteurs et affiliations

• Sellier Damien, SCION (NZL)
• Mammeri Youcef, CNRS (FRA)
• Peynaud Emilie, CIRAD-BIOS-UMR AMAP (FRA)
• Gomez-Gallego Mireia, INRAE (FRA)
• Leuzinger Sebastian, AUT (NZL)
• Dumont Yves, CIRAD-BIOS-UMR AMAP (REU) ORCID: 0000-0003-4817-685X
• Dickson Alan, SCION (NZL)
• Williams Nari, Plant and Food Research (NZL)

Source : Cirad-Agritrop (https://agritrop.cirad.fr/610190/)

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