|1. Spatial variation in filters imposed by the abiotic environment causes variation in functional
traits within and among plant species. This is abundantly clear for plant species along elevational
gradients, where parallel abiotic selection pressures give rise to predictable variation in
leaf phenotypes among ecosystems. Understanding the factors responsible for such patterns
may provide insight into the current and future drivers of biodiversity, local community
structure and ecosystem function.
2. In order to explore patterns in trait variation along elevational gradients, we conducted a
meta-analysis of published observational studies that measured three key leaf functional traits
that are associated with axes of variation in both resource competition and stress tolerance:
leaf mass:area ratio (LMA), leaf nitrogen content per unit mass (Nmass) and N content per unit
area (Narea). To examine whether there may be evidence for a genetic basis underlying the trait
variation, we conducted a review of published results from common garden experiments that
measured the same leaf traits.
3. Within studies, LMA and Narea tended to decrease with mean annual temperature (MAT)
along elevational gradients, while Nmass did not vary systematically with MAT. Correlations
among pairs of traits varied significantly with MAT: LMA was most strongly correlated with
Nmass and Narea at high-elevation sites with relatively lower MAT. The strengths of the relationships
were equal or greater within species relative to the relationships among species, suggesting
parallel evolutionary dynamics along elevational gradients among disparate biomes.
Evidence from common garden studies further suggests that there is an underlying genetic
basis to the functional trait variation that we documented along elevational gradients.
4. Taken together, these results indicate that environmental filtering both selects locally
adapted genotypes within plant species and constrains species to elevational ranges based on
their ranges of potential leaf trait values. If individual phenotypes are filtered from populations
in the same way that species are filtered from regional species pools, changing climate may
affect both the species and functional trait composition of plant communities.|