Nitrogen Enrichment and Plant Invasions: the Importance of Nitrogen-Fixing Plants and Anthropogenic Eutrophication

The invasion of natural ecosystems by exotic species is an important component of global environmental change, and poses a major threat to biodiversity. Other drivers of global change - such as alteration of the atmospheric composition and associated climate change, changing patterns of land use that fragment habitats and alter disturbance regimes, and increasing levels of airborne nitrogen deposition - also influence resource dynamics and species composition of ecosystems (Sala et al. 2000). Consequently, they all have the potential to interact with biological invasions and to accelerate this process, for which evidence is accumulating (Dukes and Mooney 1999; Mooney and Hobbs 2000). In addition, biological invasions themselves can alter the biogeochemistry of ecosystems through particular traits of the invading species (Ehrenfeld and Scott 2001). If we wish to understand and eventually predict the ecological impacts of invasive species, it is thus of particular importance to reveal the many complex interactions between all elements of global change, and their effects on ecosystem processes. In this chapter, we focus on alterations of the nitrogen cycle of terrestrial ecosystems by exotic invasions, and how nitrogen deposition may influence the success of invaders.