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Bleron, L., Duchanois, G., & Thibaut, B. (2008). Characteristic properties of embedding strength for the nailing of the gonfolio rose (Qualea rosea Aubl.). Holzforschung, 62(1), 86–90.
Abstract: Experimental results are presented with single nail joints of gonfolo rose which were loaded at different grain angles and compared to results obtained by Eurocode V. A wide range of embedding strength tests was conducted. The embedding behaviour across the grain was also investigated with a specific test apparatus. The results were analysed and modelled in terms of strength. Initial loading and unloading stiffness of the timber have been taken into account. The embedment strength of the nails varied according to the angle between the direction of loading and that to the grain. This work is part of a larger research project to establish a computer program for the prediction of stiffness and limit strengths of all timber-to-timber and timber-to-steel joints.
Keywords: embedding strength; Eurocode V; nail
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Schimann, H., Ponton, S., Hattenschwiler, S., Ferry, B., Lensi, R., Domenach, A. M., et al. (2008). Differing nitrogen use strategies of two tropical rainforest late successional tree species in French Guiana: Evidence from N-15 natural abundance and microbial activities. Soil Biol. Biochem., 40(2), 487–494.
Abstract: Previous studies in lowland tropical rainforests of French Guiana showed that, among non-N-2-fixing trees, two groups of late successional species contrasting in their leaf N-15 natural abundance coexist, suggesting two different main ways of nitrogen acquisition. Two abundant late-successional species typically co-occurring in rainforests in French Guiana, namely Eperua falcata and Dicorynia guianensis, were chosen as representative of each group. Stable isotope techniques and measurements of potentials of microbial N transformation were performed to assess to what extent leaf N-15 natural abundance of these species could be related to (i) delta N-15 signatures of soil mineral N sources and (ii) the capacity of soil to express nitrification and denitrification (both processes being directly involved in the balance between NH4+ and NO3-). Soil delta N-15-NH4+ was roughly similar to leaf delta N-15 of D. guianensis (around 3.5 parts per thousand), suggesting a preferential use of NH4+, whereas in E. falcata, leaf delta N-15 values were closer to root delta N-15-NO3- values (0.2 and -2.0 parts per thousand, respectively), suggesting a preferential use of NO3-. These differences in N source utilization were not accompanied by differences in availability in soil NO3- or in intensity of microbial functions responsible for soil N mineral evolution. However, (i) under both tree species, these functions showed clear spatial partitioning, with denitrification occurring potentially in soil and nitrification in the litter layer, and (ii) E falcata fine roots colonized the litter layer much more strongly than D. guianensis fine roots. This strongly suggests that (i) the contrasted leaf delta N-15 values found in the two late-successional species reveal distinct N acquisition strategies and (ii) the ability of roots to predominantly exploit the litter layer (E falcata) or the soil (D. guianensis) may constitute an important explanation of the observed differences. A complementarity between tree species, based on mineral N resource partitioning (itself resulting from a spatially structured location of the microbial functions responsible for the balance between NH4+ and NO3-), n thus be supposed. (c) 2007 Elsevier Ltd. All rights reserved.
Keywords: soil; litter; nitrate; nitrification; tree rooting; N-15; Eperua falcata; Dicorynia guianensis; tropical forest
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Grangier, J., Orivel, J., Negrini, M., & Dejean, A. (2008). Low intraspecific aggressiveness in two obligate plant-ant species. Insect. Soc., 55(3), 238–240.
Abstract: Little is known about the aggressiveness of plant-ants typically living in isolated trees nor about how that aggressiveness varies based on this isolation. Here, we examine intra- and interspecific aggressiveness between workers of two Allomerus species associated with two different myrmecophytes. In both cases, the level of intraspecific aggressiveness is very low whatever the distance separating the tested nests, while interspecific conflicts are always violent. Similar patterns of aggressiveness have been reported in various ant species, but the strictly arboreal life of Allomerus ants associated with the isolation of their adult colonies highlight different ecological conditions that might explain the lack of aggressiveness between conspecifics.
Keywords: aggressiveness; Allomerus; myrmecophytes; plant-ants; recognition ability
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Dejean, A., Grangier, J., Leroy, C., Orivel, J., & Gilbernau, M. (2008). Nest site selection and induced response in a dominant arboreal ant species. Naturwissenschaften, 95(9), 885–889.
Abstract: It is well known that arboreal ants, both territorially dominant species and plant ants (e.g., species associated with myrmecophytes or plants housing them in hollow structures), protect their host trees from defoliators. Nevertheless, the presence of an induced defense, suggested by the fact that the workers discovering a leaf wound recruit nestmates, is only known for plant ants. Based on the results from a field study, we show here (1) that colonies of Azteca chartifex, a territorially dominant, neotropical arboreal ant species, mostly selected Goupia glabra (Goupiaceae) trees in which to build their principal carton nests and (2) that plant signals induced workers to recruit nestmates, which patrol the leaves, likely providing the plant with a biotic defense. Furthermore, the number of recruited workers was clearly higher on G. glabra, their most frequently selected host tree species, than on other tree species. These results show that contrary to what was previously believed, induced responses are also found in territorially dominant arboreal ants and so are not limited to the specific associations between myrmecophytes and plant ants.
Keywords: ant-plant relationships; biotic defense; induced responses; predation
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Dejean, A., Moreau, C. S., Kenne, M., & Leponce, M. (2008). The raiding success of Pheidole megacephala on other ants in both its native and introduced ranges. C. R. Biol., 331(8), 631–635.
Abstract: We studied the behaviour of the invasive African myrmicine ant, Pheidole megacephala, when confronted with colonies of other common ant species in Cameroon, a part of its native range, and in Mexico, where it has been introduced. P. megacephala raided the nests of the other ants in both cases. Eleven species out of 12 put up a rather strong resistance to raiding P. megacephala workers in Cameroon compared to only three species out of 11 in Mexico, where only colonies of Solenopsis geminata, Dorymyrmex pyramicus and Dolichoderus bispinosus resisted these raids. We conclude that P. megacephala's heightened ability to successfully raid colonies of competing ants may help explain its success and the decline of native ants in areas where it has been introduced.
Keywords: invasive ants; predation; raiding other ants; recruitment
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Coutand, C., Dupraz, C., Jaouen, G., Ploquin, S., & Adam, B. (2008). Mechanical stimuli regulate the allocation of biomass in trees: Demonstration with young Prunus avium trees. Ann. Bot., 101(9), 1421–1432.
Abstract: Background and Aims Plastic tree-shelters are increasingly used to protect tree seedlings against browsing animals and herbicide drifts. The biomass allocation in young seedlings of deciduous trees is highly disturbed by common plastic tree-shelters, resulting in poor root systems and reduced diameter growth of the trunk. The shelters have been improved by creating chimney-effect ventilation with holes drilled at the bottom, resulting in stimulated trunk diameter growth, but the root deficit has remained unchanged. An experiment was set up to elucidate the mechanisms behind the poor root growth of sheltered Prunus avium trees. Methods Tree seedlings were grown either in natural windy conditions or in tree-shelters. Mechanical wind stimuli were suppressed in ten unsheltered trees by staking. Mechanical stimuli (bending) of the stem were applied in ten sheltered trees using an original mechanical device. Key Results Sheltered trees suffered from poor root growth, but sheltered bent trees largely recovered, showing that mechano-sensing is an important mechanism governing C allocation and the shoot-root balance. The use of a few artificial mechanical stimuli increased the biomass allocation towards the roots, as did natural wind sway. It was demonstrated that there was an acclimation of plants to the imposed strain. Conclusions This study suggests that if mechanical stimuli are used to control plant growth, they should be applied at low frequency in order to be most effective. The impact on the functional equilibrium hypothesis that is used in many tree growth models is discussed. The consequence of the lack of mechanical stimuli should be incorporated in tree growth models when applied to environments protected from the wind (e.g. greenhouses, dense forests).
Keywords: Prunus avium; growth; mechanical stress; bending; biomass; shoot/root ratio; wind; shelter
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Leroy, C., Jauneau, A., Quilichini, A., Dejean, A., & Orivel, J. (2008). Comparison between the anatomical and morphological structure of leaf blades and foliar domatia in the ant-plant Hirtella physophora (Chrysobalanaceae). Ann. Bot., 101(4), 501–507.
Abstract: Background and Aims Myrmecophytes, or ant-plants, are characterized by their ability to shelter colonies of some ant species in hollow structures, or ant-domatia, that are often formed by hypertrophy of the internal tissue at specific locations (i.e. trunk, branches, thorns and leaf pouches). In Hirtella physophora (Chrysobalanaceae), the focal species of this study, the ant-domatia consist of leaf pouches formed when the leaf rolls over onto itself to create two spheres at the base of the blade. Methods The morphological and anatomical changes through which foliar ant-domatia developed from the laminas are studied for the first time by using fresh and fixed mature leaves from the same H. physophora individuals. Key results Ant-domatia were characterized by larger extra-floral nectaries, longer stomatal apertures and lower stomatal density. The anatomical structure of the domatia differed in the parenchymatous tissue where palisade and spongy parenchyma were indistinct; chloroplast density was lower and lignified sclerenchymal fibres were more numerous compared with the lamina. In addition, the domatia were thicker than the lamina, largely because the parenchymatous and epidermal cells were enlarged. Conclusion Herein, the morphological and anatomical changes that permit foliar ant-domatia to be defined as a specialized leaf structure are highlighted. Similarities as well as structural modifications in the foliar ant-domatia compared with the lamina are discussed from botanical, functional and mutualistic points of view. These results are also important to understanding the reciprocal evolutionary changes in traits and, thus, the coevolutionary processes occurring in insect-plant mutualisms.
Keywords: anatomy; ant-plant mutualism; Chrysobalanaceae; extra-floral nectaries; French Guiana; Hirtella physophora; secondary domatia
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Dejean, A., Djieto-Lordon, C., & Orivel, J. (2008). The plant ant Tetraponera aethiops (Pseudomyrmecinae) protects its host myrmecophyte Barteria fistulosa (Passifloraceae) through aggressiveness and predation. Biol. J. Linnean Soc., 93(1), 63–69.
Abstract: Plant ants generally provide their host myrmecophytes (i.e. plants that shelter a limited number of ant species in hollow structures) protection from defoliating insects, but the exact nature of this protection is poorly known. It was with this in mind that we studied the association between Tetraponera aethiops F. Smith (Pseudomyrmecinae) and its specific host myrmecophyte Barteria fistulosa Mast. (Passifloraceae). Workers bore entrances into the horizontal hollow branches (domatia) of their host B. fistulosa, near the base of the petiole of the alternate horizontal leaves. They then ambush intruders from the domatia, close to these entrances. After perceiving the vibrations caused when an insect lands on a leaf, they rush to it and sting and generally spreadeagle the insect (only small caterpillars are mastered by single workers). Among the insects likely to defoliate B. fistulosa, adult leaf beetles and large katydids were taken as prey and cut up; single workers then retrieved some pieces, whereas other workers imbibed the prey's haemolymph. Other insects known to defoliate this plant, if unable to escape, were killed and discarded. Small Acrea zetes L. caterpillars were stung and then discarded by single workers; whereas locusts of different sizes were mastered by groups of workers that stung and spreadeagled them before discarding them (although a part of their haemolymph was imbibed). More workers were involved and more time was necessary to master insects taken as prey than those attacked and discarded. Consequently, the protection T. aethiops workers provide to their host B. fistulosa from defoliating insects results from predation, but more often from a type of aggressiveness wherein insects are killed and then discarded. (c) 2008 The Linnean Society of London.
Keywords: ants; plant protection; territorial aggressiveness
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Christensen-Dalsgaard, K. K., Ennos, A. R., & Fournier, M. (2008). Interrelations between hydraulic and mechanical stress adaptations in woody plants. Plant. Signal. Behav., 3(7), 463–465.
Abstract: The fields of plant water relations and plant biomechanics have traditionally been studied separately even though often the same tissues are responsible for water transport and mechanical support. There is now increasing evidence that hydraulic and mechanical adaptations may influence one another. We studied the changes in the hydraulic and mechanical properties of the wood along lateral roots of two species of buttressed trees. In these roots, the mechanical contstraints quantified by strain measurements are known to decrease distally. Further, we investigated the effect of mechanical loading on the vessel anatomy in these and four other species of tropical trees. We found that as the strain decreased, the wood became progressively less stiff and strong but the conductivity increased exponentially. This was reflected in that adaptations towards re-enforcing mechanically loaded areas resulted in xylem with fewer and smaller vessels. In addition a controlled growth experiment on three tree species showed that drought adaptation may results in plants with stronger and stiffer tissue. Our results indicate that hydraulic and mechanical stress adaptations may be interrelated, and so support recent studied suggesting that physiological responses are complex balances rather than pure optimisations. ©2008 Landes Bioscience.
Keywords: Conductivity; Modulus of elasticity; Strain; Tree ecophysiology; Tropical trees; Wood anatomy; Yield stress
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Courtois, E. A., Paine, C. E. T., Blandinieres, P. A., Stien, D., Bessiere, J. M., Houel, E., et al. (2009). Diversity of the Volatile Organic Compounds Emitted by 55 Species of Tropical Trees: a Survey in French Guiana. J. Chem. Ecol., 35(11), 1349–1362.
Abstract: Volatile organic compounds (VOCs) are produced by a broad range of organisms, from bacteria to mammals, and they represent a vast chemical diversity. In plants, one of the preeminent roles of VOCs is their repellent or cytotoxic activity, which helps the plant deter its predators. Most studies on VOCs emitted by vegetative parts have been conducted in model plant species, and little is known about patterns of VOC emissions in diverse plant communities. We conducted a survey of the VOCs released immediately after mechanical damage of the bark and the leaves of 195 individual trees belonging to 55 tropical tree species in a lowland rainforest of French Guiana. We discovered a remarkably high chemical diversity, with 264 distinct VOCs and a mean of 37 compounds per species. Two monoterpenes (alpha-pinene and limonene) and two sesquiterpenes (beta-caryophyllene and alpha-copaene), which are known to have cytotoxic and deterrent effects, were the most frequent compounds in the sampled species. As has been established for floral scents, the blend of VOCs is largely species-specific and could be used to discriminate among 43 of the 55 sampled species. The species with the most diverse blends were found in the Sapindales, Laurales, and Magnoliales, indicating that VOC diversity is not uniformly distributed among tropical species. Interspecific variation in chemical diversity was caused mostly by variation in sesquiterpenes. This study emphasizes three aspects of VOC emission by tropical tree species: the species-specificity of the mixtures, the importance of sesquiterpenes, and the wide-ranging complexity of the mixtures.
Keywords: VOCs; Chemical diversity; Sesquiterpenes; Tropical; French Guiana
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