Radial changes in wood functional traits in a rain forest from Eastern Amazonia

Trees can modify their wood structure in response to changes in mechanical, hydraulic and storage demands during their life-cycles. Thus, examining radial variations in wood traits is important to expand our knowledge of tree functioning and species ecological strategies. Yet, several aspects of radial changes in wood functional traits are still poorly understood, especially in tropical angiosperm trees. Here, we examined radial shifts in wood traits in trunks of lowland tropical forest species and explored their potential ecological implications. We measured wood specific gravity (WSG) and eight wood anatomical traits in 19 tree species with contrasting shade-tolerance. We first examined radial variations in WSG and wood anatomical traits. Then, we asked if anatomical traits drove radial variations in WSG, and whether WSG, vessel fraction and vessel composition, i.e., the ratio between vessel lumen area and number, vary independently from each other along the radius gradients. Most species had significant radials shifts in WSG and/or wood anatomical traits. Positive radial gradients in WSG were explained by different combinations of fiber and parenchyma traits, while negative radial shifts were mainly unrelated to anatomical traits. We also found that, in general, WSG, vessel fraction and vessel composition were unrelated in any radial position. This study illustrates the substantial radial variations in wood functional traits that occur in tree species from a lowland tropical forest. Our results provide valuable insights into stem allocation patterns during tree development, which would be important to increase our knowledge on tree functioning and life-history variations across coexisting species.