Alteration of Nitrogen Cycling as a Result of Invasion

Abstract

The invasion of ecosystems by non-native species may alter the nitrogen (N) cycle through different nonexclusive mechanisms. Dramatic alterations occur in an ecosystem when the invasive species possesses a new strategy to acquire this nutrient, such as N-2 fixation ability. Gradual alterations are caused by changes in the utilisation of N with respect to dominant natives, such as changes in N allocation patterns, which affect the chemical composition of tissues and therefore the decomposition and mineralisation processes. Changes in the disturbance regime mediated by plant invasion, and alteration of the trophic structure caused by the invasion of non-native animals, may also have profound effects on the N cycle. Published synthesis studies suggest that, altogether, plant invasions tend to increase N pools and to accelerate N fluxes of the invaded ecosystems. However, particular impacts are highly dependent on the context and therefore difficult to predict. A critical review of these syntheses shows that the available literature on invaders' impacts is highly biased in the selection of species, impact metrics, and ecosystem types. These biases suggest that, in spite of great advances in understanding the impacts of invaders on the N cycle, more information is needed on the impacts of many invaders so far ignored, on how invaders change the net ecosystem gains and losses of N, and on the role of the context.