Intraspecific trait variation can weaken interspecific trait correlations when assessing the whole‐plant economic spectrum

Abstract

The worldwide plant economic spectrum hypothesis predicts that leaf, stem, and root traits are correlated across vascular plant species because carbon gain depends on leaves being adequately supplied with water and nutrients, and because construction of each organ involves a trade‐off between performance and persistence. Despite its logical and intuitive appeal, this hypothesis has received mixed empirical support. If traits within species diverge in their responses to an environmental gradient, then interspecific trait correlations could be weakened when measured in natural ecosystems. To test this prediction, we measured relative growth rates (RGR) and seven functional traits that have been shown to be related to fluxes of water, nutrients, and carbon across 56 functionally diverse tree species on (1) juveniles in a controlled environment, (2) juveniles in forest understories, and (3) mature trees in forests. Leaf, stem, and fine root traits of juveniles grown in a controlled environment were closely correlated with each other, and with RGR. Remarkably, the seven leaf, stem, and fine root tissue traits spanned a single dimension of variation when measured in the controlled environment. Forest‐grown juveniles expressed lower leaf mass per area, but higher wood and fine root tissue density, than greenhouse‐grown juveniles. Traits and growth rates were decoupled in forest‐grown juveniles and mature trees. Our results indicate that constraints exist on the covariation, not just the variation, among vegetative plant organs; however, divergent responses of traits within species to environmental gradients can mask interspecific trait correlations in natural environments. Correlations among organs and relationships between traits and RGR were strong when plants were compared in a standardized environment. Our results may reconcile the discrepancies seen among studies, by showing that if traits and growth rates of species are compared across varied environments, then the interorgan trait correlations observed in controlled conditions can weaken or disappear.

Interspecific trait integration increases with environmental harshness: A case study along a metal toxicity gradient

“…The two ITI indices were calculated as follows: (a) ITI range -the range of the eigenvalues of each PCA (i.e. the difference between the eigenvalues of the first and the one of the last principal component axes) and (b) ITI sd -the standard deviation of the eigenvalues of each PCA (Cheverud, Wagner, & Dow, 1989;Laughlin et al, 2017). Since ordination eigenvalues are proportional to the overall variation of the trait correlation matrix described by the corresponding axes, two contrasting situations can be expected:…”

Seedling traits from root to shoot exhibit genetic diversity and distinct responses to environmental heterogeneity within a tree population

“…On the whole, root research has emphasised phenotypic variation among species (Laughlin , Laughlin and Messier , McCormack et al , Shipley et al , Weemstra et al , Laliberté , Laughlin et al , Erktan et al , Carvajal et al , Shen et al ), overlooking the marked intraspecific diversity in functional traits within and across communities (Ostonen et al , , Siefert et al , Defrenne et al ). From an evolutionary standpoint, a critical drawback of sampling in situ is that the effects of genetic variation and phenotypic plasticity on total phenotypic variation are confounded (Kramer‐Walter et al , Laughlin et al ), but a few experiments with a common‐garden layout show that genetic factors contribute to root variability (Velmala et al , Zadworny et al , Hamberg et al , Senior et al ). Ecological and evolutionary consequences of within‐species phenotypic and genetic diversity are noteworthy, ranging from the maintenance of species across trophic levels in a habitat (Hughes et al , Bolnick et al ) to increasing the potential of existing populations to adapt to ongoing changes in the environment (Aitken et al ).…”

“…Trait covariation could also encompass entire plants (Laughlin ): higher growth rates in the shoot may demand a boost in root proliferation that promotes nutrient uptake (Chapin ). Evidence for such expansive trait coevolution remains unsettled (Comas et al , Comas and Eissenstat , Tobner et al ), probably due to sampling in situ (Laughlin et al ) or across various taxonomic scales (Laughlin and Messier , Anderegg et al ). Thus, a common‐garden layout coupled with intensive phenotyping is convenient for the identification of trait dimensions on previously unexplored within‐species and ‐population levels.…”

Leaf drought tolerance cannot be inferred from classic leaf traits in a tropical rainforest

“…Intra‐specific variation, which may be associated with plant size, within‐canopy variation, or broader environmental gradients, may be comparable or even greater than among‐species trait variation (Li, Pei, Kéry, Niklaus, & Schmid, ; Messier, McGill, & Lechowicz, ; Poorter, Castilho, Schietti, Oliveira, & Costa, ; Siefert et al, ), and traits can present contrasting sensitivities to these scale‐dependent drivers (Messier et al, ; Rosas et al, ). Intraspecific variation can thus blur interspecific trait relationships, especially when trait values are drawn from independent studies led under various conditions (Clark et al, ; Laughlin et al, ). As an illustration, accounting for variation in tree size can substantially strengthen trait relationships across species (Medeiros et al, ).…”