Invasive plants optimize leaf nitrogen allocation in photosynthesis.

Invasive plants often outcompete co-occurring native species by expressing acquisitive functional traits that promote high photosynthetic capacity. However, it remains unclear whether these traits are newly evolved in the introduced ('away') range or if invaders arrived preadapted with superior traits from their native ('home') range. We measured photosynthetic performance of 27 invasive species in their home and away ranges, along with 17 co-occurring native species across 414 populations in temperate forest and field habitats. To understand mechanisms of photosynthetic shifts, we quantified leaf nitrogen (N) allocation among photosynthetic, structural, and defensive functions. Invasive species had greater photosynthetic capacity and photosynthetic N allocation than natives in both habitats, despite similar total leaf N. In fields, away-range invaders increased Rubisco investment compared to home populations, enhancing carboxylation rates. In forests, invaders had greater Chl allocation and quantum yield compared to native species - advantages already present in home-range populations. Increased photosynthetic N allocation was not linked to reduced structural or defensive N pools, challenging the hypothesis that invader growth advantages come at the expense of defense. Our findings suggest that enhanced N investment in photosynthesis is a common competitive advantage of invasive species, involving both away-range evolution and preadaptation.