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Intraspecific trait variation can weaken interspecific trait correlations when assessing the whole‐plant economic spectrum
Authors:Daniel C Laughlin  Christopher H Lusk  Peter J Bellingham  David F R P Burslem  Angela H Simpson  Kris R Kramer‐Walter
Institution:1. Department of Botany, University of Wyoming, Laramie, WY, USA;2. Environmental Research Institute, School of Science, University of Waikato, Hamilton, New Zealand;3. Landcare Research, Lincoln, New Zealand;4. School of Biological Sciences, University of Aberdeen, Aberdeen, UK
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.
Keywords:fine root tissue density  leaf economic spectrum  ontogenetic development  relative growth rate  root economic spectrum  wood density  wood economic spectrum
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