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Biogeographic constraints on the world-wide leaf economics spectrum

Authors


J. Mason Heberling, Department of Biology, Syracuse University, 107 College Place, Syracuse, NY 13244, USA. E-mail: jmheberl@syr.edu

ABSTRACT

Aim  The world-wide leaf economic spectrum (LES) describes tight coordination of leaf traits across global floras, reported to date as being largely independent of phylogeny and biogeography. Here, we present and test an alternative, historical perspective that predicts that biogeography places significant constraints on global trait evolution. These hypothesized constraints could lead to important deviations in leaf trait relationships between isolated floras that were influenced by different magnitudes of genetic constraint and selection.

Location  Global, including floristic regions of the Northern and Southern Hemispheres, eastern North America, East Asia (EAS), the Hawaiian Islands and tropical mainland floras.

Methods  We use a large leaf-trait database (GLOPNET) and species native distribution data to test for variation in leaf trait relationships modulated by floristic region, controlling for climatic differences. Standardized major axis analyses were used to evaluate biogeographic effects on bivariate relationships between LES traits, including relationships of photosynthetic capacity and dark respiration rate (AmassRd-mass), leaf lifespan and mass per area ratio (LL–LMA), and photosynthetic capacity and nitrogen content (AmassNmass).

Results  Independent of climate or biome, floras of different evolutionary histories exhibited different leaf trait allometries. Floras of the Northern Hemisphere exhibited greater rates of return on resource investment (steeper slopes for the trait relationships analysed), and the more diverse temperate EAS flora exhibited greater slopes or intercepts in leaf trait relationships, with the exception of the AmassNmass relationship. In contrast to our hypothesis, plants of the floristically isolated Hawaiian Islands exhibited a similar AmassNmass relationship to those of mainland tropical regions.

Main conclusions  Differences in leaf trait allometries among global floristic regions support a historical perspective in understanding leaf trait relationships and suggest that independent floras can exhibit different tradeoffs in resource capture strategies.

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