Fig. 1.

General framework for invader success in nitrogen-limited systems (Level 1). Successful invasion of species into these successional grasslands is driven by high invader carbon accrual (Level 2). In these systems, high plant carbon accumulation is dependent on the nitrogen use strategy (Level 3). Plants can maximize productivity through two nitrogen use strategies: increased carbon gain per unit plant nitrogen (Level 3a) or increased nitrogen in plant biomass (Level 3b). A plant can achieve the first strategy through two pathways: I) high proportional nitrogen allocation to leaves, or II) high carbon gain per unit leaf nitrogen. Alternatively, four possible pathways can drive an increased total plant nitrogen pool: III) high ecosystem level nitrogen inputs via nitrogen fixation; IV) low ecosystem-level nitrogen losses via leaching; V) high soil nitrogen pool turnover rate, as measured by gross nitrogen mineralization, resulting in a larger plant-available nitrogen pool; or VI) low plant nitrogen pool turnover via high leaf longevity.