|   | 
Details
   web
Records
Author (up) Levionnois, Sébastien ; Ziegler, Camille ; Heuret, Patrick ; Jansen, Steven ; Stahl, Clément ; Calvet, Emma ; Goret, Jean-Yves ; Bonal, Damien ; Coste, Sabrina
Title 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 Type Journal Article
Year 2021 Publication Annals of Forest Science Abbreviated Journal
Volume 78 Issue 4 Pages 78-87
Keywords Neotropics, bark, canopy, capacitance, drought, drought tolerance, embolism, leaves, models, transpiration, trees, tropical rain forests, xylem
Abstract 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.
Address
Corporate Author Thesis
Publisher Springer Link Place of Publication Editor
Language Summary Language Original Title
Series Editor Series Title Abbreviated Series Title
Series Volume Series Issue Edition
ISSN ISBN Medium
Area Expedition Conference
Notes Approved no
Call Number EcoFoG @ webmaster @ Serial 1034
Permanent link to this record
 

 
Author (up) Maréchaux, I.; Bonal, D.; Bartlett, M.K.; Burban, B.; Coste, S.; Courtois, E.A.; Dulormne, M.; Goret, J.-Y.; Mira, E.; Mirabel, A.; Sack, L.; Stahl, C.; Chave, J.
Title Dry-season decline in tree sapflux is correlated with leaf turgor loss point in a tropical rainforest Type Journal Article
Year 2018 Publication Functional Ecology Abbreviated Journal Funct Ecol
Volume 32 Issue 10 Pages 2285-2297
Keywords drought tolerance; hydraulic conductance; sap flow; sapflux density; tropical trees; turgor loss point; water potential; wilting point
Abstract Water availability is a key determinant of forest ecosystem function and tree species distributions. While droughts are increasing in frequency in many ecosystems, including in the tropics, plant responses to water supply vary with species and drought intensity and are therefore difficult to model. Based on physiological first principles, we hypothesized that trees with a lower turgor loss point (pi-tlp), that is, a more negative leaf water potential at wilting, would maintain water transport for longer into a dry season. We measured sapflux density of 22 mature trees of 10 species during a dry season in an Amazonian rainforest, quantified sapflux decline as soil water content decreased and tested its relationship to tree pi-tlp, size and leaf predawn and midday water potentials measured after the onset of the dry season. The measured trees varied strongly in the response of water use to the seasonal drought, with sapflux at the end of the dry season ranging from 37 to 117% (on average 83 +/- 5 %) of that at the beginning of the dry season. The decline of water transport as soil dried was correlated with tree pi-tlp (Spearman's rho > 0.63), but not with tree size or predawn and midday water potentials. Thus, trees with more drought-tolerant leaves better maintained water transport during the seasonal drought. Our study provides an explicit correlation between a trait, measurable at the leaf level, and whole-plant performance under drying conditions. Physiological traits such as pi-tlp can be used to assess and model higher scale processes in response to drying conditions.
Address
Corporate Author Thesis
Publisher Wiley/Blackwell (10.1111) Place of Publication Editor
Language Summary Language Original Title
Series Editor Series Title Abbreviated Series Title
Series Volume Series Issue Edition
ISSN 0269-8463 ISBN Medium
Area Expedition Conference
Notes doi: 10.1111/1365-2435.13188 Approved no
Call Number EcoFoG @ webmaster @ Serial 830
Permanent link to this record
 

 
Author (up) Svensk, M.; Coste, S.; Gérard, B.; Gril, E.; Julien, F.; Maillard, P.; Stahl, C.; Leroy, C.
Title Drought effects on resource partition and conservation among leaf ontogenetic stages in epiphytic tank bromeliads Type Journal Article
Year 2020 Publication Physiologia Plantarum Abbreviated Journal Physiol. Plant.
Volume 170 Issue 4 Pages 488-507
Keywords chlorophyll; nitrogen; water; Bromeliaceae; drought; metabolism; photosynthesis; plant leaf; Bromeliaceae; Chlorophyll; Droughts; Nitrogen; Photosynthesis; Plant Leaves; Water
Abstract Studying the response to drought stress of keystone epiphytes such as tank bromeliads is essential to better understand their resistance capacity to future climate change. The objective was to test whether there is any variation in the carbon, water and nutrient status among different leaf ontogenetic stages in a bromeliad rosette subjected to a gradient of drought stress. We used a semi-controlled experiment consisting in a gradient of water shortage in Aechmea aquilega and Lutheria splendens. For each bromeliad and drought treatment, three leaves were collected based on their position in the rosette and several functional traits related to water and nutrient status, and carbon metabolism were measured. We found that water status traits (relative water content, leaf succulence, osmotic and midday water potentials) and carbon metabolism traits (carbon assimilation, maximum quantum yield of photosystem II, chlorophyll and starch contents) decreased with increasing drought stress, while leaf soluble sugars and carbon, nitrogen and phosphorus contents remained unchanged. The different leaf ontogenetic stages showed only marginal variations when subjected to a gradient of drought. Resources were not reallocated between different leaf ontogenetic stages but we found a reallocation of soluble sugars from leaf starch reserves to the root system. Both species were capable of metabolic and physiological adjustments in response to drought. Overall, this study advances our understanding of the resistance of bromeliads faced with increasing drought stress and paves the way for in-depth reflection on their strategies to cope with water shortage. © 2020 Scandinavian Plant Physiology Society
Address Laboratoire Ecologie Fonctionnelle et Environnement, Université de Toulouse, CNRS, Toulouse, 31062, France
Corporate Author Thesis
Publisher Blackwell Publishing Ltd Place of Publication Editor
Language Summary Language Original Title
Series Editor Series Title Abbreviated Series Title
Series Volume Series Issue Edition
ISSN 00319317 (Issn) ISBN Medium
Area Expedition Conference
Notes PDF trop gros voir la documentaliste – merci Approved no
Call Number EcoFoG @ webmaster @ Serial 943
Permanent link to this record
 

 
Author (up) Verryckt, L.T.; Ellsworth, D.S.; Vicca, S.; Van Langenhove, L.; Peñuelas, J.; Ciais, P.; Posada, J.M.; Stahl, C.; Coste, S.; Courtois, E.A.; Obersteiner, M.; Chave, J.; Janssens, I.A.
Title Can light-saturated photosynthesis in lowland tropical forests be estimated by one light level? Type Journal Article
Year 2020 Publication Biotropica Abbreviated Journal Biotropica
Volume 52 Issue 6 Pages 1183-1193
Keywords canopy architecture; interspecific variation; light intensity; lowland environment; parameter estimation; photon flux density; photosynthesis; saturation; tropical forest; French Guiana
Abstract Leaf-level net photosynthesis (An) estimates and associated photosynthetic parameters are crucial for accurately parameterizing photosynthesis models. For tropical forests, such data are poorly available and collected at variable light conditions. To avoid over- or underestimation of modeled photosynthesis, it is critical to know at which photosynthetic photon flux density (PPFD) photosynthesis becomes light-saturated. We studied the dependence of An on PPFD in two tropical forests in French Guiana. We estimated the light saturation range, including the lowest PPFD level at which Asat (An at light saturation) is reached, as well as the PPFD range at which Asat remained unaltered. The light saturation range was derived from photosynthetic light-response curves, and within-canopy and interspecific differences were studied. We observed wide light saturation ranges of An. Light saturation ranges differed among canopy heights, but a PPFD level of 1,000 µmol m−2 s−1 was common across all heights, except for pioneer trees species that did not reach light saturation below 2,000 µmol m−2 s−1. A light intensity of 1,000 µmol m−2 s−1 sufficed for measuring Asat of climax species at our study sites, independent of the species or the canopy height. Because of the wide light saturation ranges, results from studies measuring Asat at higher PPFD levels (for upper canopy leaves up to 1,600 µmol m−2 s−1) are comparable with studies measuring at 1,000 µmol m−2 s−1. © 2020 The Association for Tropical Biology and Conservation
Address UMR 5174, Laboratoire Evolution et Diversité Biologique, CNRS, Université Paul Sabatier, Toulouse, France
Corporate Author Thesis
Publisher Blackwell Publishing Ltd Place of Publication Editor
Language Summary Language Original Title
Series Editor Series Title Abbreviated Series Title
Series Volume Series Issue Edition
ISSN 00063606 (Issn) ISBN Medium
Area Expedition Conference
Notes Approved no
Call Number EcoFoG @ webmaster @ Serial 948
Permanent link to this record
 

 
Author (up) Verryckt, L.T.; Van Langenhove, L.; Ciais, P.; Courtois, E.A.; Vicca, S.; Peñuelas, J.; Stahl, C.; Coste, S.; Ellsworth, D.S.; Posada, J.M.; Obersteiner, M.; Chave, J.; Janssens, I.A.
Title Coping with branch excision when measuring leaf net photosynthetic rates in a lowland tropical forest Type Journal Article
Year 2020 Publication Biotropica Abbreviated Journal Biotropica
Volume 52 Issue 4 Pages 608-615
Keywords branch cutting; canopy physiology; French Guiana; gas exchange; photosynthesis; rainforest; stomatal conductance; ecological modeling; environmental conditions; forest canopy; leaf; measurement method; photosynthesis; tree; tropical forest; Gruidae
Abstract Measuring leaf gas exchange from canopy leaves is fundamental for our understanding of photosynthesis and for a realistic representation of carbon uptake in vegetation models. Since canopy leaves are often difficult to reach, especially in tropical forests with emergent trees up to 60 m at remote places, canopy access techniques such as canopy cranes or towers have facilitated photosynthetic measurements. These structures are expensive and therefore not very common. As an alternative, branches are often cut to enable leaf gas exchange measurements. The effect of branch excision on leaf gas exchange rates should be minimized and quantified to evaluate possible bias. We compared light-saturated leaf net photosynthetic rates measured on excised and intact branches. We selected branches positioned at three canopy positions, estimated relative to the top of the canopy: upper sunlit foliage, middle canopy foliage, and lower canopy foliage. We studied the variation of the effects of branch excision and transport among branches at these different heights in the canopy. After excision and transport, light-saturated leaf net photosynthetic rates were close to zero for most leaves due to stomatal closure. However, when the branch had acclimated to its new environmental conditions—which took on average 20 min—light-saturated leaf net photosynthetic rates did not significantly differ between the excised and intact branches. We therefore conclude that branch excision does not affect the measurement of light-saturated leaf net photosynthesis, provided that the branch is recut under water and is allowed sufficient time to acclimate to its new environmental conditions. © 2020 The Association for Tropical Biology and Conservation
Address UMR 5174 Laboratoire Evolution et Diversité Biologique, Université Paul Sabatier, CNRS, Toulouse, France
Corporate Author Thesis
Publisher Blackwell Publishing Ltd Place of Publication Editor
Language Summary Language Original Title
Series Editor Series Title Abbreviated Series Title
Series Volume Series Issue Edition
ISSN 00063606 (Issn) ISBN Medium
Area Expedition Conference
Notes Approved no
Call Number EcoFoG @ webmaster @ Serial 960
Permanent link to this record