Resolving whole‐plant economics from leaf, stem and root traits of 1467 Amazonian tree species

Abstract

It remains unclear how evolutionary and ecological processes have shaped the wide variety of plant life strategies, especially in highly diverse ecosystems like tropical forests. Some evidence suggests that species have diversified across a gradient of ecological strategies, with different plant tissues converging to optimize resource use across environmental gradients. Alternative hypotheses propose that species have diversified following independent selection on different tissues, resulting in a decoupling of trait syndromes across organs. To shed light on the subject, we assembled an unprecedented dataset combining 19 leaf, stem and root traits for 1467 tropical tree species inventoried across 71 0.1‐ha plots spanning broad environmental gradients in French Guiana. Nearly 50% of the overall functional heterogeneity was expressed along four orthogonal dimensions, after accounting for phylogenetic dependences among species. The first dimension related to fine root functioning, while the second and third dimensions depicted two decoupled leaf economics spectra, and the fourth dimension encompassed a wood economics spectrum. Traits involved in orthogonal functional strategies, five leaf traits in particular but also trunk bark thickness, were consistently associated with a same gradient of soil texture and nutrient availability. Root traits did not show any significant association with edaphic variation, possibly because of the prevailing influence of other factors (mycorrhizal symbiosis, phylogenetic constraints). Our study emphasises the existence of multiple functional dimensions that allow tropical tree species to optimize their performance in a given environment, bringing new insights into the debate around the presence of a whole plant economic spectrum in tropical forest tree communities. It also emphasizes the key role that soil heterogeneity plays in shaping tree species assembly. The extent to which different organs are decoupled and respond to environmental gradients may also help to improve our predictions of species distribution changes in responses to habitat modification and environmental changes.

High intraspecific growth variability despite strong evolutionary heritage in a neotropical forest

“…Future research on the role of root traits in tropical tree growth is thus particularly promising given that tropical forests harbour the greatest diversity of root characteristics (Ma et al ., 2018). Interestingly, species growth potential is better predicted by the combination of traits from roots, wood and leaf, in accordance with the idea of multiple functional dimensions that allow tropical tree species to optimise their performance in a given environment Vleminckx et al . (2021), while participating together in a whole plant economic spectrum (Reich 2014).…”

“…Using the 120 species in common with Vleminckx et al . (2021), we found six functional traits explaining an important part of variation in species growth potential (40%).…”

“…Finally, root traits also predicted species growth potential with fast-growing species investing less in their root systems with decreased fine roots diameters and higher specific root length, as already shown for temperate species (Comas, Bouma and Eissenstat 2002, Comas and Eissenstat 2004) but never in the tropics, in the limit of our knowledge. Soil heterogeneity can be expected to play a key role in shaping root traits (Vleminckx et al ., 2021), while the dynamics of forest gaps cannot be excluded either (Xiang et al ., 2013).…”

“…We also tested the link between functional traits and species growth using the mean values of the 120 species of Vleminckx et al (2021) shared with our study. Vleminckx et al (2021) functional data included 19 leaf, stem and root traits.…”

Rethinking the nature of intraspecific variability and its consequences on species coexistence

“…Such differences between species have then been specified and quantified through traits that drive each species response to the environment (species functional traits, McGill et al 2006; Westoby & Wright 2006). Similar to the environment that presents highly-dimensional variation at local scales, these functional species differences spread along many dimensions within communities (Hutchinson 1957, 1959, Baraloto et al 2010b, Kraft et al 2015, Rüger et al 2018, Maréchaux et al 2020, Vleminckx et al 2021). The adaptive significance of trait differences between species is widely appreciated (Westoby and Wright 2006, Falster et al 2017); many of these species traits could never have evolved if they did not contribute to species fitness.…”