Isohydricity and hydraulic isolation explain reduced hydraulic failure risk in an experimental tree species mixture

Moreno Myriam, Simioni Guillaume, Cochard Hervé, Doussan Claude, Guillemot Joannès, Decarsin Renaud, Fernández-Conradi Pilar, Dupuy Jean-Luc, Trueba Santiago, Pimont François, Ruffault Julien, Jean Frederic, Marloie Olivier, Martin-StPaul Nicolas K.. 2024. Isohydricity and hydraulic isolation explain reduced hydraulic failure risk in an experimental tree species mixture. Plant Physiology:kiae239 : 1-15.

https://doi.org/10.1093/plphys/kiae239

Article de revue ; Article de recherche ; Article de revue à facteur d'impact

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Résumé : Species mixture is promoted as a crucial management option to adapt forests to climate change. However, there is little consensus on how tree diversity affects tree water stress, and the underlying mechanisms remain elusive. By using a greenhouse experiment and a soil-plant-atmosphere hydraulic model, we explored whether and why mixing the isohydric Aleppo pine (Pinus halepensis, drought avoidant) and the anisohydric holm oak (Quercus ilex, drought tolerant) affects tree water stress during extreme drought. Our experiment showed that the intimate mixture strongly alleviated Q. ilex water stress while it marginally impacted P. halepensis water stress. Three mechanistic explanations for this pattern are supported by our modeling analysis. First, the difference in stomatal regulation between species allowed Q. ilex trees to benefit from additional soil water in mixture, thereby maintaining higher water potentials and sustaining gas exchange. By contrast, P. halepensis exhibited earlier water stress and stomatal regulation. Second, P. halepensis trees showed stable water potential during drought, although soil water potential strongly decreased, even when grown in a mixture. Model simulations suggested that hydraulic isolation of the root from the soil associated with decreased leaf cuticular conductance was a plausible explanation for this pattern. Third, the higher predawn water potentials for a given soil water potential observed for Q. ilex in mixture can—according to model simulations—be explained by increased soil-to-root conductance, resulting from higher fine root length. This study brings insights into the mechanisms involved in improved drought resistance of mixed species forests.

Mots-clés Agrovoc : résistance à la sécheresse, adaptation aux changements climatiques, stress dû à la sécheresse, système racinaire, changement climatique, échange gazeux, Ilex, potentiel hydrique des racines, eau du sol, tolérance à la sécheresse, Pinus halepensis, physiologie végétale, potentiel hydrique

Mots-clés libres : Forest, Functional diversity, Drought resistance, Tree hydraulic, Safety margins

Agences de financement hors UE : Agence de l'Environnement et de la Maîtrise de l'Energie, Agence Nationale de la Recherche, Institut National de Recherche pour l'Agriculture, l'Alimentation et l'Environnement

Projets sur financement : (FRA) Mixed Forest plantations for climate Change mitigation and adaptation., (FRA) L'eau totale disponible pour l'arbre : un paramètre clé, manquant pour évaluer la vulnérabilité du fonctionnement des forêts face au changement climatique, (FRA) Adaptation to Climate Change in Agriculture and Forestry

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