A central aim of invasion biology has been to identify key functional differences between native and non-native species to determine which traits may be responsible for invasion success and the impacts of invasion. There are two primary ways that differences may exist between native and non-native species. The traits of the species pools may differ, or the way that the traits interact with their environment may differ between native and non-native taxa. Leaf nutrient concentrations are functional traits that directly link to plant metabolic processes and can be critical in understanding plant invasions and their role in plant community dynamics. To relate leaf nutrient concentrations to successional community assembly and invasion, we sampled healthy, mature leaves from 122 native and exotic species across a wide range of successional statuses in a mesic old-field assemblage in New Jersey, USA. Variation in the native and non-native species pools were examined within growth forms (graminoid, forb, and woody) to ensure appropriate comparisons. Leaf nutrient concentration data (carbon, nitrogen, phosphorus, potassium, magnesium, and calcium) were paired with long-term (57 year) community dynamics from the Buell-Small Succession Study to evaluate abundance-weighted trait values over succession for native and exotic species.
Results/Conclusions
After accounting for nutrient differences across growth forms, there were minimal differences based on plant origin, with only leaf carbon lower and leaf potassium higher in non-native species. However, these differences were not sufficient to generate overall differences between native and non-native species in multivariate analyses. In contrast to the overall similarity in leaf nutrient concentrations in the species pools, the temporal trajectories of the abundance-weighted trait values for all leaf nutrients except magnesium differed strongly between native and exotic plants in succession. While this pattern may be partially attributable to variation in the species pool for carbon and potassium, successional processes generated differential sorting on the remaining leaf nutrients, suggesting underlying differences in how the same traits function between native and non-native taxa. Overall, the non-native communities tended to have greater representation of higher macronutrient concentration species, during at least part of the successional sequence. These results suggest that both variation in the species pool and variation in the successional selection of plant traits generate functional differences between native and non-native plants. Regardless of their origin, variation in leaf nutrient chemistry between native and exotic plants in succession has important implications for nutrient dynamics in invaded habitats.