Intégration des voies de transport de l’eau dans un érable : réponses du flux de sève à une ablation de branche

Abstract

Keywords:Acer platanoides / flux distribution / heat field deformation method / integrated pipes / multi-point sensors / stem xylem functional structure Abstract • It has been known for a long time that sectored and integrated patterns of vascular systems exist in different species and even within the same tree, depending on its age and history. However, very few publications consider the topology of the vascular pathways between roots and branches.• Some results on this important aspect of the vascular system are presented in this paper. They have been obtained with adult maple trees by directly studying the water movement in the stem and root xylem with the heat field deformation (HFD) method for sap flow measurements.• Multi-point HFD sensors were installed at different heights of a Norway maple tree (Acer platanoides L.) along its stem axis. Single-point HFD sensors were installed in three small lateral roots of another sample maple. Experimental treatments (branch severing) triggered changes in sap movement in the stem and root sapwood.• The sample trees belong to the group with an integrated transport system ("integrated pipes"), sharing stem space on both sides of the tree to supply two large parts of the crown with water from each root sector. Nevertheless, conducting pathways had their autonomy for axial transport and the pipe model theory describes the vascular system of the studied trees well. Thus, the integration of axial transport in the stem xylem should presumably occur through the cross-grained network of axial vessels. Mots-clés :Acer platanoides / distribution du flux / méthode de déformation du champ de chaleur / tuyaux intégrés / capteurs multi-points / structure fonctionnelle du xylème de la tige Résumé -Intégration des voies de transport de l'eau dans un érable : réponses du flux de sève à une ablation de branche.• Il est connu depuis longtemps que des modèles sectorisés et intégrés de système vasculaire coexistent chez différentes espèces et même dans un arbre unique, en fonction de son âge et de l'histoire. Cependant, très peu de publications ont examiné la topologie du parcours vasculaire entre les racines et les branches.• Quelques résultats sur cet aspect important du système vasculaire sont présentés ici. Ils ont été obtenus avec des érables adultes en étudiant directement le mouvement de l'eau dans le xylème de la tige et de la racine avec la méthode de déformation du champ de chaleur (HFD) pour mesurer le flux de sève.• Des capteurs HFD-multi-points ont été installés à différentes hauteurs dans un érable plane (Acer platanoïdes L.) le long de la tige. Des capteurs HFD-simple-point ont été installés dans trois petites racines latérales d'un autre érable. Des traitements expérimentaux (ablation de branche) ont déclen-ché des changements dans la circulation de la sève dans l'aubier de la tige et de la racine.• Les arbres échantillonnés présentent un système vasculaire intégré (« tuyaux intégrés »), avec un tronc partagé en deux secteurs alimentant les deux grandes parties de la couron...

Modeling the influence of differential sectoriality on the photosynthetic responses of understory saplings to patchy light and water availability

“…In large trees, sectoriality has been shown to depend not only on intervessel pitting (Orians et al 2004;Ellmore et al 2006) but also on ''cross-grained'' drift of vessels with height up the tree (Tyree and Zimmerman 2002;Kitin et al 2004). While intervessel pitting constrains flow between sectors in the presence of a hydraulic gradient, as is represented by our model, cross-grained drift is expected to result in tangential spread of resources independent of such a gradient (Nadezhdina 2010). Empirical work will be required to determine the applicability of the model in trees displaying substantial drift, and it should be noted that the frequency of drift in younger trees has not been established.…”

“…This approach contrasts with more detailed xylem network models (e.g. Loepfe et al 2007), in that we vary a single sectoriality parameter to capture overall patterns in tangential hydraulic resistance, without delving into anatomical details, such as the degree to which these patterns depend on vessel-to-vessel lateral connections and the presence of ''cross-grained'' vessels (Tyree and Zimmerman 2002;Orians et al 2004;Nadezhdina 2010). Our purpose is to establish general expectations for the relationship between sectoriality and photosynthesis, to inform future empirical research.…”

Revisiting the Heat Field Deformation (HFD) method for measuring sap flow

“…These methods which depend on heat transfer, however, differ fairly widely in their capabilities and limitations, notably in their sensitivity to low, zero and reverse flow rates. Reverse sap flow is particularly important for understanding the whole plant physiology and tree architecture, and acts as an indicator of hydraulic redistribution (Nadezhdina 1999, 2010, Burgess et al 1998. In thermodynamic methods, thermometers are commonly used to gauge temperature changes of the heat field around a heater in response to sap movement.…”

A one-dimensional model of water flow in soil-plant systems based on plant architecture

“…The model may be also helpful to describe the impact of different distributions of conductivity values along the tree architecture in particular of larger trees to study their role in protecting the xylem against cavitation, while maintaining transpirational water flow. This description may lead to a better understanding of observed differences in xylem structures and functions between deep and shallow roots, roots, stem and branches (Nadezhdina 2010;North 2004) and of the relevance of nonxylary pathways for water uptake and transpiration (Sperry et al 2003). The model may also be applied to better describe differences of stand water budgets between mixed forest stands of different species composition.…”