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Levionnois, Sébastien ; Ziegler, Camille ; Heuret, Patrick ; Jansen, Steven ; Stahl, Clément ; Calvet, Emma ; Goret, Jean-Yves ; Bonal, Damien ; Coste, Sabrina |
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Is vulnerability segmentation at the leaf‑stem transition a drought resistance mechanism? A theoretical test with a trait‑based model for Neotropical canopy tree species |
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Journal Article |
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2021 |
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Annals of Forest Science |
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78 |
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4 |
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78-87 |
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Neotropics, bark, canopy, capacitance, drought, drought tolerance, embolism, leaves, models, transpiration, trees, tropical rain forests, xylem |
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Leaf-stem vulnerability segmentation predicts lower xylem embolism resistance in leaves than stem. However, although it has been intensively investigated these past decades, the extent to which vulnerability segmentation promotes drought resistance is not well understood. Based on a trait-based model, this study theoretically supports that vulnerability segmentation enhances shoot desiccation time across 18 Neotropical tree species. CONTEXT: Leaf-stem vulnerability segmentation predicts lower xylem embolism resistance in leaves than stems thereby preserving expensive organs such as branches or the trunk. Although vulnerability segmentation has been intensively investigated these past decades to test its consistency across species, the extent to which vulnerability segmentation promotes drought resistance is not well understood. AIMS: We investigated the theoretical impact of the degree of vulnerability segmentation on shoot desiccation time estimated with a simple trait-based model. METHODS: We combined data from 18 tropical rainforest canopy tree species on embolism resistance of stem xylem (flow-centrifugation technique) and leaves (optical visualisation method). Measured water loss under minimum leaf and bark conductance, leaf and stem capacitance, and leaf-to-bark area ratio allowed us to calculate a theoretical shoot desiccation time (tcᵣᵢₜ). RESULTS: Large degrees of vulnerability segmentation strongly enhanced the theoretical shoot desiccation time, suggesting vulnerability segmentation to be an efficient drought resistance mechanism for half of the studied species. The difference between leaf and bark area, rather than the minimum leaf and bark conductance, determined the drastic reduction of total transpiration by segmentation during severe drought. CONCLUSION: Our study strongly suggests that vulnerability segmentation is an important drought resistance mechanism that should be better taken into account when investigating plant drought resistance and modelling vegetation. We discuss future directions for improving model assumptions with empirical measures, such as changes in total shoot transpiration after leaf xylem embolism. |
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EcoFoG @ webmaster @ |
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1034 |
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Levionnois, S.; Jansen, S.; Wandji, R.T.; Beauchêne, J.; Ziegler, C.; Coste, S.; Stahl, C.; Delzon, S.; Authier, L.; Heuret, P. |
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Linking drought-induced xylem embolism resistance to wood anatomical traits in Neotropical trees |
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Journal Article |
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2021 |
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New Phytologist |
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New Phytol. |
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229 |
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3 |
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1453-1466 |
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bordered pits; drought-induced embolism; pit membrane; transmission electron microscopy; tropical trees; vessel grouping; xylem anatomy |
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Drought-induced xylem embolism is considered to be one of the main factors driving mortality in woody plants worldwide. Although several structure–functional mechanisms have been tested to understand the anatomical determinants of embolism resistance, there is a need to study this topic by integrating anatomical data for many species. We combined optical, laser, and transmission electron microscopy to investigate vessel diameter, vessel grouping, and pit membrane ultrastructure for 26 tropical rainforest tree species across three major clades (magnoliids, rosiids, and asteriids). We then related these anatomical observations to previously published data on drought-induced embolism resistance, with phylogenetic analyses. Vessel diameter, vessel grouping, and pit membrane ultrastructure were all predictive of xylem embolism resistance, but with weak predictive power. While pit membrane thickness was a predictive trait when vestured pits were taken into account, the pit membrane diameter-to-thickness ratio suggests a strong importance of the deflection resistance of the pit membrane. However, phylogenetic analyses weakly support adaptive coevolution. Our results emphasize the functional significance of pit membranes for air-seeding in tropical rainforest trees, highlighting also the need to study their mechanical properties due to the link between embolism resistance and pit membrane diameter-to-thickness ratio. Finding support for adaptive coevolution also remains challenging. © 2020 The Authors New Phytologist © 2020 New Phytologist Foundation |
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UMR BIOGECO, INRAE, Université de Bordeaux, Pessac, 33615, France |
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Blackwell Publishing Ltd |
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0028646x (Issn) |
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EcoFoG @ webmaster @ |
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997 |
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Levionnois, Sébastien ; Salmon, Camille ; Alméras, Tancrède ; Clair, Bruno ; Ziegler, Camille ; Coste, Sabrina ; Stahl, Clement ; Gonzalez-Melo, Andrés ; Heinz, Christine ; Heuret, Patrick |
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Anatomies, vascular architectures, and mechanics underlying the leaf size-stem size spectrum in 42 Neotropical tree species |
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2021 |
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Journal of Experimental Botany |
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72 |
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22 |
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7957–7969 |
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The leaf size-stem size spectrum is one of the main dimensions of plant ecological strategies. Yet the anatomical, mechanical, and hydraulic implications of small vs. large shoots are still poorly understood. We investigated 42 tropical rainforest tree species in French Guiana, with a wide range of leaf areas at the shoot level. We quantified the scaling of hydraulic and mechanical constraints with shoot size estimated as the water potential difference ΔΨ and the bending angle ΔΦ, respectively. We investigated how anatomical tissue area, flexural stiffness and xylem vascular architecture affect such scaling by deviating (or not) from theoretical isometry with shoot size variation. Vessel diameter and conductive path length were found to be allometrically related to shoot size, thereby explaining the independence between ΔΨ and shoot size. Leaf mass per area, stem length, and the modulus of elasticity were allometrically related with shoot size, explaining the independence between ΔΦ and shoot size. Our study also shows that the maintenance of both water supply and mechanical stability across the shoot size range are not in conflict. |
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Oxford University Press |
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EcoFoG @ webmaster @ |
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1050 |
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Levionnois, S.; Coste, S.; Nicolini, E.; Stahl, C.; Morel, H.; Heuret, P. |
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Scaling of petiole anatomies, mechanics and vasculatures with leaf size in the widespread Neotropical pioneer tree species Cecropia obtusa Trécul (Urticaceae) |
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Journal Article |
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2020 |
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Tree physiology |
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Tree Physiol. |
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40 |
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2 |
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245-258 |
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allometry; leaf size; petiole anatomy; scaling; theoretical hydraulic conductivity; vessel widening; xylem |
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Although the leaf economic spectrum has deepened our understanding of leaf trait variability, little is known about how leaf traits scale with leaf area. This uncertainty has resulted in the assumption that leaf traits should vary by keeping the same pace of variation with increases in leaf area across the leaf size range. We evaluated the scaling of morphological, tissue-surface and vascular traits with overall leaf area, and the functional significance of such scaling. We examined 1,271 leaves for morphological traits, and 124 leaves for anatomical and hydraulic traits, from 38 trees of Cecropia obtusa Trécul (Urticaceae) in French Guiana. Cecropia is a Neotropical genus of pioneer trees that can exhibit large laminas (0.4 m2 for C. obtusa), with leaf size ranging by two orders of magnitude. We measured (i) tissue fractions within petioles and their second moment of area, (ii) theoretical xylem hydraulic efficiency of petioles and (iii) the extent of leaf vessel widening within the hydraulic path. We found that different scaling of morphological trait variability allows for optimisation of lamina display among larger leaves, especially the positive allometric relationship between lamina area and petiole cross-sectional area. Increasing the fraction of pith is a key factor that increases the geometrical effect of supportive tissues on mechanical rigidity and thereby increases carbon-use efficiency. We found that increasing xylem hydraulic efficiency with vessel size results in lower leaf lamina area: xylem ratios, which also results in potential carbon savings for large leaves. We found that the vessel widening is consistent with hydraulic optimisation models. Leaf size variability modifies scaling of leaf traits in this large-leaved species. © The Author(s) 2020. Published by Oxford University Press. All rights reserved. For permissions, please email: journals.permission@oup.com. |
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UMR AMAP, CIRAD, CNRS, IRD, Université de Montpellier, Montpellier, 34398, France |
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NLM (Medline) |
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Export Date: 16 March 2020 |
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EcoFoG @ webmaster @ |
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921 |
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Levionnois, S.; Tysklind, N.; Nicolini, E.; Ferry, B.; Troispoux, V.; Le Moguedec, G.; Morel, H.; Stahl, C.; Coste, S.; Caron, H.; Heuret, P. |
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Soil variation response is mediated by growth trajectories rather than functional traits in a widespread pioneer Neotropical tree |
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2020 |
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bioRxiv, peer-reviewed by Peer Community in Ecology |
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351197 |
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v4 |
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Trait-environment relationships have been described at the community level across tree species. However, whether interspecific trait-environment relationships are consistent at the intraspecific level is yet unknown. Moreover, we do not know how consistent is the response between organ vs. whole-tree level.We examined phenotypic variability for 16 functional leaf (dimensions, nutrient, chlorophyll) and wood traits (density) across two soil types, Ferralitic Soil (FS) vs. White Sands (WS), on two sites for 70 adult trees of Cecropia obtusa Trécul (Urticaceae) in French Guiana. Cecropia is a widespread pioneer Neotropical genus that generally dominates early successional forest stages. To understand how soil types impact resource-use through the processes of growth and branching, we examined the architectural development with a retrospective analysis of growth trajectories. We expect soil types to affect both, functional traits in relation to resource acquisition strategy as already described at the interspecific level, and growth strategies due to resource limitations with reduced growth on poor soils.Functional traits were not involved in the soil response, as only two traits-leaf residual water content and K content-showed significant differences across soil types. Soil effects were stronger on growth trajectories, with WS trees having the slowest growth trajectories and less numerous branches across their lifespan.The analysis of growth trajectories based on architectural analysis improved our ability to characterise the response of trees with soil types. The intraspecific variability is higher for growth trajectories than functional traits for C. obtusa, revealing the complementarity of the architectural approach with the functional approach to gain insights on the way trees manage their resources over their lifetime. Soil-related responses of Cecropia functional traits are not the same as those at the interspecific level, suggesting that the effects of the acting ecological processes are different between the two levels. Apart from soil differences, much variation was found across sites, which calls for further investigation of the factors shaping growth trajectories in tropical forests. |
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EcoFoG @ webmaster @ |
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931 |
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