Functional traits are often used as species-specific means in trait-based predictions of ecosystem processes, assuming that interspecific differences are greater than intraspecific trait variation. Although this assumption is increasingly challenged, there is lack of knowledge regarding the extent to which intraspecific trait variation in response to varying environmental conditions depends on the considered traits and the characteristics of the studied species. In a new study published in AoB PLANTS, Siebenkäs et al. grew eight perennial grassland species representing two functional groups (grasses vs. forbs) and growth statures (small vs. tall) under different light and nutrient availability. The strength of trait variation in response to resource availability differed among functional groups and growth statures in many aboveground traits, while being more consistent in belowground traits. The results, showing the dependency of trait-based species ranking on environmental conditions, limit the applicability of species-specific mean trait values in ecological studies.
