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Community 15N isoscapes: a spatially-explicit method for tracing plant-plant-interactions

Christine Hellmann1, Katherine G. Rascher2, Cristina Máguas3, Christiane Werner2
1 Agroecosystem/Functional Ecosystem Research, University of Bayreuth, Experimental and Systems Ecology, University of Bielefeld, Germany
2 Agroecosystem/Functional Ecosystem Research, University of Bayreuth
3 Centre for Environmental Biology, University of Lisbon, Portugal

P 3.10 in Ecosystems: Function and Services


Isoscapes, i.e. spatially continuous observations of variations in stable isotope ratios, have greatly improved our ability to understand biogeochemical processes on continental to global scales. Additionally, isoscapes may be a valuable tool for resolving the spatial component of plant-plant-interactions within communities. For example, exotic plant invaders often strongly impact native species performance by altering ecosystem functioning of the systems they invade, particularly regarding water-, carbon- and nutrient-cycles. However, the spatial extent of such alterations is largely unknown.

Here we show that substantial N input by the N2-fixing exotic invasive Acacia longifolia to a nutrient poor Portuguese dune system can be traced using spatially resolved information on native plants’ leaf δ15N. N isotopic signatures of the native system (δ15N ≈ -10‰) differed strongly from the atmospherically derived N in A. longifolia phyllodes (δ15N ≈ 0‰)a. Thus, sources of N for native plants could be readily distinguished. Leaf δ15N of a native, non-fixing species was increasingly enriched the closer the plant grew to the invader, indicating uptake of N derived from decaying A. longifolia litter. The enrichment was evident far beyond the stands of the invader, demonstrating that A. longifolia affected N budgets of native species up to a distance of 8 m exceeding the margin of the canopy. Furthermore, using the isoscapes approach, we were able to quantify the total area of N enrichment and could thus show that the area affected by invasion was at least 3.5 times larger than the area actually occupied by the invaderb. However, a native N2-fixing species had no such effects.

Thus, downscaling isoscapes to the community level opens new frontiers in quantifying the spatial dimension of functional changes associated with plant invasions. Moreover, considering the feasibility and applicability of this approach, it may provide a promising tool to identify, quantify and monitor different types of functional plant-plant interactions within communities at a spatially explicit scale.



a Hellmann C, Sutter R, Rascher KG, Máguas C, Correia O, Werner C (2011) Impact of an exotic N2-fixing Acacia on composition and N status of a native Mediterranean community. Acta Oecologica 37: 43-50, doi:10.1016/j.actao.2010.11.005.

b Rascher KG, Hellmann C, Máguas C, Werner C (2012) Community scale 15N isoscapes: tracing the spatial impact of an exotic N2-fixing invader. Ecology Letters 15: 484-491, doi: 10.1111/j.1461-0248.2012.01761.x.

last modified 2012-09-28