Community scale 15N isoscapes: tracing the spatial impact of an exotic N2 -fixing invader.

Plant-plant interactions are key processes shaping plant communities, but methods are lacking to accurately capture the spatial dimension of these processes. Isoscapes, i.e. spatially continuous observations of variations in stable isotope ratios, provide innovative methods to trace the spatial dimension of ecological processes at continental to global scales. Herein, we test the usefulness of nitrogen isoscapes (δ(15) N) for quantifying alterations in community functioning following exotic plant invasion. Nitrogen introduced by an exotic N(2) -fixing acacia could be accurately traced through the ecosystem and into the surrounding native vegetation by combining native species foliar δ(15) N with spatial information regarding plant location using geostatistical methods. The area impacted by N-addition was at least 3.5-fold greater than the physical area covered by the invader. Thus, downscaling isoscapes to the community level opens new frontiers in quantifying the spatial dimension of functional changes associated with invasion and in resolving the spatial component of within-community interactions.