Conclusions
Our study improves the understanding of intraspecific trait variation
along environmental gradients, showing that the underlying ecological
and evolutionary mechanisms differ between reproductive and vegetative
traits of P. lanceolata . The environmental structuring of
variation in biomass-corrected reproductive traits was retained in
common greenhouse conditions, indicative of genetic differentiation. In
contrast, vegetative traits showed strong plastic responses to buffer
short-term environmental variation, sometimes in opposition to genetic
differentiation. Differences between vegetative and reproductive traits
seem to arise due to the different relationship between each type of
trait and overall fitness. These results provide a crucial insight into
the potential uses and limitations of observational data, which is
readily available for a considerable number of species and traits, but
which may provide more uncertain information than common-garden
experiments. While genetic differentiation was accurately predicted from
observational trait-environment relationships for biomass-corrected
reproductive traits, it was sometimes masked for vegetative traits by
phenotypic plasticity and countergradient variation. Thus, evaluating
evolutionary responses to environment from observational data may lead,
in the case of vegetative traits or traits not closely related with
fitness, to underestimate the capacity of plants to adapt to new
environmental conditions. We also advocate for considering biomass
dependency in trait variation analyses, as well as the implications of
species life histories on trait-fitness relationships. In view of the
general call for including intraspecific trait variation in ecological
models (Moran et al . 2016, Funk et al . 2017), these
considerations are important for a more informed prediction of species
responses to global change.