Invasive Buddleja davidii allocates more nitrogen to its photosynthetic machinery than five native woody species

The general-purpose genotype hypothesis and the hypothesis of the evolution of invasiveness predict that invasive species are characterized by particular traits that confer invasiveness. However, these traits are still not well-defined. In this study, ecophysiological traits of eight populations of the invasive shrub Buddleja davidii from a wide range of European locations and five co-occurring native woody species in Germany were compared in a common garden experiment. We hypothesized that the invader has higher resource capture ability and utilization efficiency than the natives. No differences were detected among the eight populations of B. davidii in any of the traits evaluated, indicating that the invader did not evolve during range expansion, thus providing support to the general-purpose genotype hypothesis. The invader showed significantly higher maximum electron transport rate, maximum carboxylation rate, carboxylation efficiency, light-saturated photosynthetic rate (Pmax) and photosynthetic nitrogen utilization efficiency (PNUE) than the five natives. Leaf nitrogen content was not significantly different between the invader and the natives, but the invader allocated more nitrogen to the photosynthetic machinery than the natives. The increased nitrogen content in the photosynthetic machinery resulted in a higher resource capture ability and utilization efficiency in the invader. At the same intercellular CO2 concentration, Pmax was significantly higher in the invader than in the natives, again confirming the importance of the higher nitrogen allocation to photosynthesis. The invader reduced metabolic cost by increasing the ratio of Pmax to dark respiration rate (Rd), but it did not reduce carbon cost by increasing the specific leaf area and decreasing leaf construction cost. The higher nitrogen allocation to the photosynthetic machinery, Pmax, PNUE and Pmax/Rd may facilitate B. davidii invasion, although studies involving a wide range of invasive species are needed to understand the generality of this pattern and to fully assess the ecological advantages afforded by these features.