For the past 50 years there has been rapid warming in the maritime Antarctic, with concurrent, and probably temperature-mediated, proliferation of the two native plants, Antarctic pearlwort (Colobanthus quitensis) and especially Antarctic hair grass (Deschampsia antarctica). In many terrestrial ecosystems at high latitudes, nitrogen (N) supply regulates primary productivity. Although the predominant view is that only inorganic and amino acid N are important sources of N for angiosperms, most N enters soil as protein. Maritime Antarctic soils have large stocks of proteinaceous N, which is released slowly as decomposition is limited by low temperatures. Consequently, an ability to acquire N at an early stage of availability is key to the success of photosynthetic organisms. Here we show that D. antarctica can acquire N through its roots as short peptides, produced at an early stage of protein decomposition, acquiring N over three times faster than as amino acid, nitrate or ammonium, and more than 160 times faster than the mosses with which it competes. Efficient acquisition of the N released in faster decomposition of soil organic matter as temperatures rise may give D. antarctica an advantage over competing mosses that has facilitated its recent proliferation in the maritime Antarctic.