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Biwolé, A.B.; Dainou, K.; Fayolle, A.; Hardy, O.J.; Brostaux, Y.; Coste, S.; Delion, S.; Betti, J.L.; Doucet, J.-L. |
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Title |
Light Response of Seedlings of a Central African Timber Tree Species, Lophira alata (Ochnaceae), and the Definition of Light Requirements |
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Journal Article |
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Year |
2015 |
Publication |
Biotropica |
Abbreviated Journal |
Biotropica |
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Volume |
47 |
Issue |
6 |
Pages |
681-688 |
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Keywords  |
biomass allocation; Central Africa; light requirement: Lophira alata; population; relative growth rate; seedling growth; timber species; Afrique centrale; allocation de biomasse; besoins en lumière; croissance des semis; bois d'œuvre; Lophira alata; population; taux de croissance relatif |
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Light is of primary importance in structuring tropical tree communities. Light exposure at seedling and adult stages has been used to characterize the ecological profile of tropical trees, with many implications in forest management and restoration ecology. Most shade-tolerance classification systems have been proposed based on empirical observations in a specific area and thus result in contradictions among categories assigned to a given species. In this study, we aimed to quantify the light requirements for seedling growth of a Central African timber tree, Lophira alata (Ochnaceae), taking into account effects of population origin. In two controlled experiments: a light response experiment and a comparative population experiment, conducted in southwestern Cameroon, using seeds collected from four populations (three from Cameroon and one from Gabon), we examined the quantitative responses to irradiance of seedlings. After 2 years, mortality was very low (<3%), even in extremely low irradiance. Growth and biomass allocation patterns varied in response to light, with intermediate irradiance (24–43%) providing optimal conditions. Light response differed between populations. The Boumba population in the northeastern edge of the species' distribution exhibited the highest light requirements, suggesting a local adaptation. As a result of positive growth at low irradiance and maximum growth at intermediate irradiance, we concluded that L. alata exhibits characteristics of both non-pioneer and pioneer species. Implications of our results to propose an objective way to assign the light requirement for tropical tree species are discussed. |
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1744-7429 |
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EcoFoG @ webmaster @ |
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648 |
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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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Title |
Linking drought-induced xylem embolism resistance to wood anatomical traits in Neotropical trees |
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Journal Article |
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Year |
2021 |
Publication |
New Phytologist |
Abbreviated Journal |
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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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. |
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Title |
Coping with branch excision when measuring leaf net photosynthetic rates in a lowland tropical forest |
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Journal Article |
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2020 |
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Biotropica |
Abbreviated Journal |
Biotropica |
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52 |
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4 |
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608-615 |
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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 |
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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 |
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UMR 5174 Laboratoire Evolution et Diversité Biologique, Université Paul Sabatier, CNRS, Toulouse, France |
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Blackwell Publishing Ltd |
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00063606 (Issn) |
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EcoFoG @ webmaster @ |
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960 |
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Bonal, D.; Born, C.; Brechet, C.; Coste, S.; Marcon, E.; Roggy, J.C.; Guehl, J.M. |
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The successional status of tropical rainforest tree species is associated with differences in leaf carbon isotope discrimination and functional traits |
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Journal Article |
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2007 |
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Annals of Forest Science |
Abbreviated Journal |
Ann. For. Sci. |
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64 |
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2 |
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169-176 |
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Keywords |
C-13; functional diversity; leaf gas exchange; species grouping; tropical rainforest |
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We characterised the among species variability in leaf gas exchange and morphological traits under controlled conditions of seedlings of 22 tropical rainforest canopy species to understand the origin of the variability in leaf carbon isotope discrimination (Delta) among species with different growth and dynamic characteristics (successional gradient). Our results first suggest that these species pursue a consistent strategy in terms of. throughout their ontogeny (juveniles grown here versus canopy adult trees from the natural forest). Second, leaf Delta was negatively correlated with WUE and N, and positively correlated with g(s), but among species differences in Delta were mainly explained by differences in WUE. Finally, species belonging to different successional groups display distinct leaf functional and morphological traits. We confirmed that fast growing early successional species maximise carbon assimilation with high stomatal conductance. In contrast, fast and slow growing late successional species are both characterised by low carbon assimilation values, but by distinct stomatal conductance and leaf morphological features. Along the successional gradient, these differences result in much lower Delta for the intermediate species (i.e. fast growing late successional) as compared to the two other groups. |
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INRA Kourou, UMR Ecol Forets Guyane, F-97387 Kourou, Guyane, France, Email: damien.bonal@kourou.cirad.fr |
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EDP SCIENCES S A |
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1286-4560 |
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ISI:000244438100006 |
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EcoFoG @ eric.marcon @ |
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169 |
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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. |
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Can light-saturated photosynthesis in lowland tropical forests be estimated by one light level? |
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Journal Article |
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2020 |
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Biotropica |
Abbreviated Journal |
Biotropica |
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52 |
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6 |
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1183-1193 |
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canopy architecture; interspecific variation; light intensity; lowland environment; parameter estimation; photon flux density; photosynthesis; saturation; tropical forest; French Guiana |
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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 |
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UMR 5174, Laboratoire Evolution et Diversité Biologique, CNRS, Université Paul Sabatier, Toulouse, France |
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Blackwell Publishing Ltd |
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00063606 (Issn) |
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EcoFoG @ webmaster @ |
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948 |
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