Ruelle, J., Beauchene, J., Thibaut, A., & Thibaut, B. (2007). Comparison of physical and mechanical properties of tension and opposite wood from ten tropical rainforest trees from different species. Ann. For. Sci., 64(5), 503–510.
Abstract: On 10 trees from 10 species of French Guyana tropical rainforest in a clear active process of restoring verticality growth strains were measured in situ in order to determine the occurrence of tension wood within samples. Wood specimens were cut in the vicinity of the growth strains measurements in order to measure some mechanical and physical properties. As suspected, tensile growth strains was very much higher in tension wood zone, because longitudinal modulus of elasticity was slightly higher. Longitudinal shrinkage was also much higher in tension wood than in opposite wood.
Keywords: tension wood; opposite wood; tropical rainforest; physical and mechanical properties
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Scotti, I., Paglia, G., Magni, F., & Morgante, M. (2006). Population genetics of Norway spruce (Picea abies Karst.) at regional scale: sensitivity of different microsatellite motif classes in detecting differentiation. Ann. For. Sci., 63(5), 485–491.
Abstract: Four populations of Norway spruce (Picea abies Karst.) were screened using nine nuclear microsatellite markers (three trinucleotides and six dinucleotides) and four chloroplast markers (all mononucleotides). Marker classes were compared for their variability, mutation rate and ability to detect differentiation between stands. Dinucleotide markers proved to be the most variable group and chloroplast stretches the least variable, with differences in mutation rate between the former and the latter spanning over two orders of magnitude. Variability correlated to the number of repeats but not to the absolute length of the microsatellite region. The different marker classes were combined with two different measures of genetic distance in order to investigate the performance of markers and evolutionary models for the study of genetic variation in natural populations of Norway spruce. Weir and Cockeram's F-ST generally performed better in this clear-cut, four-population model study. Chloroplast haplotypes turned out to be the most sensitive marker system, being able to differentiate populations and to detect differences in genetic variability between sub-regions.
Keywords: conifers; SSR; divergence; statistical testing; genetic distance
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Almeras, T., Yoshida, M., & Okuyama, T. (2006). The generation of longitudinal maturation stress in wood is not dependent on diurnal changes in diameter of trunk. J. Wood Sci., 52(5), 452–455.
Abstract: A hypothetical mechanism for the generation of maturation stress in wood was tested experimentally. The hypothesis was that the maturation stress could partly originate in a physical mechanism related to daily changes in water pressure and associated diurnal strains. The matrix of lignin and hemicellulose, deposited in the cell wall during the night, would be put in compression by the effect of water tension during the next day. The cellulose framework, crystallizing during the day, would be put in tension by the decrease in tension at night and subsequent cell-wall swelling. This was tested on young saplings of sugi and beech. Half of the saplings were submitted to continuous lighting, which canceled diurnal strains. Saplings were tilted 40 degrees, and their uprighting movement was measured. The uprighting movement is directly due to the production of reaction wood and the concomitant development of large longitudinal maturation stress. It occurred in the continuously lighted plants at least as much as in control plants. We conclude that the generation of longitudinal maturation stress in tension or compression wood is not directly related to variations in water pressure and diurnal strains.
Keywords: maturation stress; growth stress; cell-wall maturation; continuous lighting; diurnal strains
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Clair, B., Almeras, T., & Sugiyama, J. (2006). Compression stress in opposite wood of angiosperms: observations in chestnut, mani and poplar. Ann. For. Sci., 63(5), 507–510.
Abstract: In order to face environmental constraints, trees are able to re-orient their axes by controlling the stress level in the newly formed wood layers. Angiosperms and gymnosperms evolved into two distinct mechanisms: the former produce a wood with large tension pre-stress on the upper side of the tilted axis, while the latter produce a wood with large compression pre-stress on the lower side. In both cases, the difference between this stress level and that of the opposite side, in light tension, generates the bending of the axis. However, light values of compression were sometimes measured in the opposite side of angiosperms. By analysing old data on chestnut and mani and new data on poplar, this study shows that these values were not measurement artefacts. This reveals that generating light compression stress in opposite wood contributes to improve the performance of the re-orientation mechanism.
Keywords: reaction wood; compression wood; tension wood; opposite wood; plant biomechanics; growth stresses; microfibrils angle
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Eva, H. D., Belward, A. S., De Miranda, E. E., Di Bella, C. M., Gond, V., Huber, O., et al. (2004). A land cover map of South America. Glob. Change Biol., 10(5), 731–744.
Abstract: A digital land cover map of South America has been produced using remotely sensed satellite data acquired between 1995 and the year 2000. The mapping scale is defined by the 1 km spatial resolution of the map grid-cell. In order to realize the product, different sources of satellite data were used, each source providing either a particular parameter of land cover characteristic required by the legend, or mapping a particular land cover class. The map legend is designed both to fit requirements for regional climate modelling and for studies on land cover change. The legend is also compatible with a wider, global, land cover mapping exercise, which seeks to characterize the world's land surface for the year 2000. As a first step, the humid forest domain has been validated using a sample of high-resolution satellite images. The map demonstrates both the major incursions of agriculture into the remaining forest domains and the extensive areas of agriculture, which now dominate South America's grasslands.
Keywords: Amazonia; ecosystems; land cover; mapping; South America; vegetation classes
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Roggy, J. C., Moiroud, A., Lensi, R., & Domenach, A. M. (2004). Estimating N transfers between N-2-fixing actinorhizal species and the non-N-2-fixing Prunus avium under partially controlled conditions. Biol. Fertil. Soils, 39(5), 312–319.
Abstract: Two methods of N transfer between plants-by litter decomposition and root-to-root exchange-were examined in mixed plantations of N-fixing and non-fixing trees. Nitrogen transfers from decaying litters were measured by placing N-15-labelled litters from four actinorhizal tree species around shoots of containerized Prunus avium. Nitrogen transfers by root-to-root exchanges were measured after foliar NO3-N-15 fertilization of Alnus subcordata and Elaeagnus angustifolia growing in containers in association with P. avium. During the first 2 years of litter decomposition, from 5-20% of the N, depending on the litter identity, was released and taken up by P. avium. N availability in the different litters was strongly correlated with the amount of water-soluble N, which was highest in leaves of E. angustifolia. In the association between fixing and non-fixing plants, 7.5% of the A. subcordata N and 25% of E. angustifolia N was transferred to P. avium by root exchange. These results showed that the magnitude of N transfers by root exchange depended on the associated N-2-fixing species. Among the species investigated, E. angustifolia displayed the highest capacity for exudating N from roots as well as for releasing N from litters. These qualities make this tree a promising species for enhancing wood yields in mixed stands.
Keywords: actinorhizal trees; mixed culture; litter; N transfer by roots; N-15
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Latouche-Halle, C., Ramboer, A., Bandou, E., Caron, H., & Kremer, A. (2004). Long-distance pollen flow and tolerance to selfing in a neotropical tree species. Mol. Ecol., 13(5), 1055–1064.
Abstract: Outcrossing rates, pollen dispersal and male mating success were assessed in Dicorynia guianensis Amshoff, a neotropical tree endemic to the Guiana shield. All adult trees within a continuous area of 40 ha (n = 157) were mapped, and were genotyped with six microsatellite loci. In addition, progenies were genotyped from 22 mature trees. At the population level, the species was mostly outcrossing (t(m) = 0.89) but there was marked variation among individuals. One tree exhibited mixed mating, confirming earlier results obtained with isozymes that D. guianensis can tolerate selfing. A Bayesian extension of the fractional paternity method was used for paternity analysis, and was compared with the neighbourhood method used widely for forest trees. Both methods indicated that pollen dispersal was only weakly related to distance between trees within the study area, and that the majority (62%) of pollen came from outside the study stand. Using maximum likelihood, male potential population size was estimated to be 1119, corresponding to a neighbourhood size of 560 hectares. Male mating success was, however, related to the diameter of the stem and to flowering intensity assessed visually. The mating behaviour of D. guianensis is a combination of long-distance pollen flow and occasional selfing. The species can still reproduce when it is extremely rare, either by selfing or by dispersing pollen at long distances. These results, together with the observation that male mating success was correlated with the size of the trees, could be implemented in management procedures aiming at regenerating the species.
Keywords: Dicorynia guianensis; microsatellites; outcrossing rate; pollen flow; reproductive success; tropical tree
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Gond, V., Bartholome, E., Ouattara, F., Nonguierma, A., & Bado, L. (2004). Monitoring and mapping of waters and wetlands in arid regions using the SPOT-4 VEGETATION imaging system. Int. J. Remote Sens., 25(5), 987–1004.
Abstract: Monitoring the state of small waterbodies and wetlands is very useful in dry regions, because their existence is entirely controlled by the rhythm of local rainfall. On VEGETATION image colour composites, waterbodies and marshy vegetation show up clearly. Yet simple image classification does not yield sufficiently good results because 'spectral signatures' vary significantly together with the ecological conditions of these surfaces. A robust contextual procedure taking into account local contrast was successfully developed and tested. A systematic validation was carried out and a map of waterbodies and wetlands was produced for Burkina Faso and neighbouring regions.
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Sobotnik, J., Sillam-Dusses, D., Weyda, F., Dejean, A., Roisin, Y., Hanus, R., et al. (2010). The frontal gland in workers of Neotropical soldierless termites. Naturwissenschaften, 97(5), 495–503.
Abstract: The presence of the frontal gland is well established in termite soldiers of Rhinotermitidae, Serritermitidae, and Termitidae. It is one of their main defensive adaptations or even an exclusive weapon. The gland was also occasionally reported in alate imagoes, but never in the worker caste. Here, we report the first observation of a frontal gland in workers of several Neotropical and one African species of Apicotermitinae. The ultrastructure of Aparatermes cingulatus and Anoplotermes nr. subterraneus is described in detail. In these two species, the gland is well-developed, functional and consists of class 1 secretory cells. The presence of envelope cells, wrapping the gland, is an unusual feature, as well as the presence of several zonulae adherens, connecting neighbouring glandular cells. The frontal gland of workers is homologous to this organ in soldiers and imagoes, as evidenced by the same position in the head and its connection to the same muscle. However, the defensive role of the frontal gland in workers remains to be confirmed.
Keywords: Frontal gland; Workers; Soldierless termites; Apicotermitinae; Anoplotermes; Aparatermes
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Fanin, N., Hattenschwiler, S., Barantal, S., Schimann, H., & Fromin, N. (2011). Does variability in litter quality determine soil microbial respiration in an Amazonian rainforest? Soil Biol. Biochem., 43(5), 1014–1022.
Abstract: Tree species-rich tropical rainforests are characterized by a highly variable quality of leaf litter input to the soil at small spatial scales. This diverse plant litter is a major source of energy and nutrients for soil microorganisms, particularly in rainforests developed on old and nutrient-impoverished soils. Here we tested the hypothesis that the variability in leaf litter quality produced by a highly diverse tree community determines the spatial variability of the microbial respiration process in the underlying soil. We analyzed a total of 225 litter-soil pairs from an undisturbed Amazonian rainforest in French Guiana using a hierarchical sampling design. The microbial respiration process was assessed using substrate-induced respiration (SIR) and compared to a wide range of quality parameters of the associated litter layer (litter nutrients, carbon forms, stoichiometry, litter mass and pH). The results show that the variability of both litter quality and SIR rates was more important at large than at small scales. SIR rates varied between 1.1 and 4.0 μg h(-1) and were significantly correlated with litter layer quality (up to 50% of the variability explained by the best mixed linear model). Total litter P content was the individual most important factor explaining the observed spatial variation in soil SIR, with higher rates associated to high litter P. SIR rates also correlated positively with total litter N content and with increasing proportions of labile C compounds. However, contrary to our expectation, SIR rates were not related to litter stoichiometry. These data suggest that in the studied Amazonian rainforest, tree canopy composition is an important driver of the microbial respiration process via leaf litter fall, resulting in potentially strong plant-soil feedbacks. (C) 2011 Elsevier Ltd. All rights reserved.
Keywords: Carbon forms; French Guiana; Litter quality; Microbial respiration process; Nitrogen; Phosphorus; Stoichiometry
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