Abstract: · Context and aim This study aimed to examine the effect of the tension wood G-layer on the viscoelastic properties of wood. · Methods Tension wood and opposite wood samples were obtained from six French Guianese tropical rainforest species (Sextonia rubra, Ocotea guyanensis, Inga alba, Tachigali melinoni, Iyranthera sagotiana and Virola michelii); the tension wood of the former three of these species had a Glayer, whilst the tension wood from the latter three had no Glayer. Tensile dynamic mechanical analysis (DMA) was performed on green never dried wood samples in the longitudinal direction with samples submerged in a water bath at a temperature (30°C) and frequency (1 Hz) representative of the conditions experienced by wood within a living tree. Then, DMA was repeated with samples conditioned to an air-dried state. Finally, samples were oven-dried to measure longitudinal shrinkage. · Results Tension wood did not always have a higher longitudinal storage (elastic) modulus than opposite wood from the same tree regardless of the presence or absence of a G-layer. For the species containing a G-layer, tension wood had a higher damping coefficient and experienced a greater longitudinal shrinkage upon drying than opposite wood from the same species. No difference was found in damping coefficients between tension wood and opposite wood for the species that had no G-layer. · Conclusion It is proposed that the different molecular composition of the G-layer matrix has an influence on the viscoelasticity of wood, even if a biomechanical gain is not yet clear. This study shows that rheological properties and longitudinal shrinkage can be used to detect the presence of a G-layer in tension wood. © INRA/Springer-Verlag France 2011.

Abstract: The symbiotic interactions between Frankia strains and their associated plants from the Casuarinaceae under controlled conditions are well documented but little is known about these interactions under natural conditions. We explored the symbiotic interactions between eight genotypically characterized Frankia strains and five Casuarinaceae species in long-term field trials. Characterization of strains was performed using the polymerase chain reaction (PCR) and restriction fragment length polymorphism (RFLP) for the nifD-nifK intergenic transcribed spacer (ITS) and 16S-23S ITS. Assessments of the symbiotic interactions were based on nodulation patterns using nodule dry weight and viability, and on actual N-2 fixation using the delta N-15 method. The PCR-RFLP patterns showed that the analyzed strains belonged to the same genotypic group (CeD group), regardless of the host species and environment of origin. The nodule viability index is introduced as a new tool to measure the viability of perennial nodules and to predict their effectiveness. The host Casuarinaceae species was a key factor influencing both the actual N-2-fixing activity of the associated Frankia strain and the viability of nodules within a location. This is the first study providing information on the symbiotic interactions between genotypically characterized Frankia strains and actinorhizal plants under natural conditions. The results revealed a way to improve a long-term management of the Casuarinaceae symbiosis.

Abstract: Nucleotide diversity was assessed within nine candidate genes (in total 4.6 kb) for the time of bud burst in nine sessile oak (Quercus petraea) populations distributed in central and northern Europe. The sampled populations were selected on the basis of their contrasting time of bud burst observed in common garden experiments (provenance tests). The candidate genes were selected according to their expression profiles during the transition from quiescent to developing buds and/or their functional role in model plants. The overall nucleotide diversity was large (pi(tot) – 6.15 x 10(-3); pi(silent) – 11.2 x 10(-3)), but population differentiation was not larger than for microsatellites. No outlier single-nucleotide polymorphism (SNP), departing from neutral expectation, was found among the total of 125 SNPs. These results contrasted markedly with the significant associations that were observed between the candidate genes and bud burst in segregating populations. Quantitative trait loci (QTLs) for bud burst were identified for 13 year*site seasonal observations in a cloned mapping pedigree. Nineteen QTLs were detected, and QTLs located on linkage groups 2, 5 and 9 contributed repeatedly to more than 12% of the phenotypic variation of the trait. Eight genes were polymorphic in the two parents of the pedigree and could be mapped on the existing genetic map. Five of them located within the confidence intervals of QTLs for bud burst. Interestingly, four of them located within the three QTLs exhibiting the largest contributions to bud burst. Heredity (2010) 105, 401-411; doi:10.1038/hdy.2009.170; published online 9 December 2009

Abstract: The identity of the dominant root-associated microbial symbionts in a forest determines the ability of trees to access limiting nutrients from atmospheric or soil pools 1,2 , sequester carbon 3,4 and withstand the effects of climate change 5,6 . Characterizing the global distribution of these symbioses and identifying the factors that control this distribution are thus integral to understanding the present and future functioning of forest ecosystems. Here we generate a spatially explicit global map of the symbiotic status of forests, using a database of over 1.1 million forest inventory plots that collectively contain over 28,000 tree species. Our analyses indicate that climate variables—in particular, climatically controlled variation in the rate of decomposition—are the primary drivers of the global distribution of major symbioses. We estimate that ectomycorrhizal trees, which represent only 2% of all plant species 7 , constitute approximately 60% of tree stems on Earth. Ectomycorrhizal symbiosis dominates forests in which seasonally cold and dry climates inhibit decomposition, and is the predominant form of symbiosis at high latitudes and elevation. By contrast, arbuscular mycorrhizal trees dominate in aseasonal, warm tropical forests, and occur with ectomycorrhizal trees in temperate biomes in which seasonally warm-and-wet climates enhance decomposition. Continental transitions between forests dominated by ectomycorrhizal or arbuscular mycorrhizal trees occur relatively abruptly along climate-driven decomposition gradients; these transitions are probably caused by positive feedback effects between plants and microorganisms. Symbiotic nitrogen fixers—which are insensitive to climatic controls on decomposition (compared with mycorrhizal fungi)—are most abundant in arid biomes with alkaline soils and high maximum temperatures. The climatically driven global symbiosis gradient that we document provides a spatially explicit quantitative understanding of microbial symbioses at the global scale, and demonstrates the critical role of microbial mutualisms in shaping the distribution of plant species. © 2019, The Author(s), under exclusive licence to Springer Nature Limited.

Abstract: We propose new methods for evaluating the spatial distribution of firms. To assess whether firms are concentrated or dispersed, economists have traditionally used indices that analyse the heterogeneity of a spatial structure at a single geographic level. We introduce distance-based methods, Besag's L function (derived from Ripley's K function) and Diggle and Chetwynd's D function to describe simultaneously spatial distribution at different geographical scales. Our empirical applications consider the distribution of French manufacturing firms in the Paris area and in France generally. For some geographic levels, results show significant concentration or dispersion of firms according to their sector of activity.