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Anatomical traits underlying stem and root wood density in contrasting Αmazonian forests

Thursday, 27 June 2013: 08:30
La Paz - B West (Herradura San Jose)
Claire Fortunel , UMR Ecofog, INRA, France
Julien Ruelle , UMR Lerfob, INRA, France
Jacques Beauchene , UMR Ecofog, CIRAD, France
Paul V.A. Fine , Integrative Biology, University of California, Berkeley
Christopher Baraloto , INRA, UMR EcoFoG, French Guiana
Wood density has emerged as a central trait to comprehend variations in the performance of tree species across environmental gradients, but it is a complex trait encompassing various functions (conduction, support, storage). Still lacking is an understanding of how different wood anatomical elements contribute to variation in wood density across tropical forests. Here we examined key traits describing stem and woody root density and anatomy in white sand, clay terra firme and seasonally flooded forests in French Guiana, that represent the gradient of soil fertility, drought and flooding stress, forest structure, and floristic compositions found throughout the Amazon region. We measured 31 traits describing stem and woody roots in 148 individuals from 113 species that represented the 15 most abundant species in each habitat and species from seven monophyletic lineages. Principal component analysis revealed three axes of coordinated traits that were consistent when including phylogenetically independent contrasts: a first axis (27.80%) defined by stem and wood vessel traits, with second and third axes (22.74 and 14.13%) defined by wood density and structural traits of root and stem respectively. This suggests that fiber, fiber wall and lumen fractions are major contributors to wood density. White sand species had the most dense stem and root tissues, followed by clay terra firme species and seasonally flooded species, the latest having the least dense tissues. White sand species also had higher stem fiber fraction, but lower stem lumen and parenchyma fractions than seasonally flooded species. We found evidence for strong evolutionary constraints on stem and root wood density and anatomy, with significant differences among phylogenetic lineages for all traits, but without any interactions with habitat for most traits. We conclude that biomechanical explanations for tree distribution across environmental gradients in the Amazon should receive more attention in future studies.