Coordination between leaf and root traits in Mediterranean coastal dune plants.

Plant trait-based functional spectra are crucial to assess ecosystem functions and services. Whilst most research has focused on aboveground vegetative traits (leaf economic spectrum, LES), contrasting evidence on any coordination between the LES and root economic spectrum (RES) has been reported. Studying spectra variation along environmental gradients and accounting for species' phylogenetic relatedness may help to elucidate the strength of coordination between above- and belowground trait variation. We focused on leaf and root traits of 39 species sampled in 3 distinct habitats (front, back and slack) along a shoreline-inland gradient on coastal dunes. We tested within a phylogenetic comparative framework for the presence of the LES and RES, and eventually a coordination between these spectra exploring whether it is related to a variation in ecological strategies along this gradient. In each habitat, three-quarter of trait variation is captured in two-dimensional spectra with species' phylogenetic relatedness moderately influencing coordination and trade-off between traits. Along the ecological gradient, aboveground traits support the LES in all habitats. Belowground traits are consistent with the RES in the back-habitat only, where the environmental constraints are weaker, in which a coordination between leaf and root traits was also found, supporting the whole-plant spectrum (PES). This study confirms the complexity to seek any correlation between the LES and RES in ecosystems characterized by multiple environmental pressures as those investigated here. Changes in traits adopted to resist environmental constrains are similar among species independently from their evolutionary relatedness, explaining the low phylogenetic contribution in supporting our results.