No evidence for larger leaf trait plasticity in ecological generalists compared to specialists

Aim: Phenotypic plasticity is hypothesized to contribute to a species' capacity to occupy broader ranges of conditions and to optimally exploit resource-rich environments. Although this is supported by case studies of individual species, we do not know whether larger plasticity in functional traits is generally associated with ecological characteristics of species such as their niche breadth or niche position. Here, we test whether there is such a relationship for plasticity in leaf functional traits. Location: Central Europe. Methods: We surveyed 110-132 grassland plant species for plasticity in five leaf traits [leaf thickness, leaf greenness, specific leaf area, leaf dry matter content (LDMC) and plant height] and for biomass changes in response to experimental fertilization, shading and waterlogging. Trait plasticity and changes in biomass were compared with species niche characteristics along three environmental axes (light, nutrient and soil moisture) derived from a vegetation-plot database. Results: Although response of several traits to experimental treatments correlated with niche position and breadth (change in leaf thickness, greenness and biomass in response to fertilization; change in LDMC due to shading; and change in plant height and biomass due to waterlogging), we did not find evidence that species with broader niches or species from resource-rich environments are more plastic. Ecological generalists even turned out to be less plastic in some traits, including leaf thickness after fertilization and waterlogging. Generalists also displayed smaller plastic response averaged across all five traits ('composite plasticity'), though the relationship was not statistically significant. This composite plasticity was positively related to absolute change in biomass in all experimental treatments. Main conclusions: Our results suggest that larger species-level plasticity in leaf traits is not necessarily associated with a capacity to occupy a broader range of environments or with growth in resource-rich habitats; rather, it may indicate species' sensitivity to environmental changes.