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

Abstract

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.

Genetic diversity and differentiation of invasive <i>Acacia longifolia</i> in Portugal

“…Since its introduction, this species has invaded many adjacent environments including Pinus pinaster plantations, which has a high economic impact (Fernandes et al, 2015). A. longifolia's invasive success in Portugal is such that, in spite of its fairly recent introduction some 130 years ago, it can be found throughout the country where it is negatively impacting the diversity of native species (Marchante et al, 2003) and ecosystem functioning (Rascher et al, 2012;Ulm et al, 2017) such as changes in plant diversity (Holmes and Cowling, 1997;Lorenzo et al, 2012;Lazzaro et al, 2014), soil composition (Marchante et al, 2008;Souza-Alonso et al, 2015) and water availability (Lorenzo and Rodríguez-Echeverría, 2015).…”

Relationship between recruitment and mother plant vitality in the alien species Acacia cyclops A. Cunn. ex G. Don

“…Higher soil moisture and nutrients (N and C) content may considerably increase the chance for seedlings to survive and evolve into saplings. For instance, an overwhelming capability by Acacia longifolia to modify the environment, and especially nitrogen supply within plant communities, in driving the invasion processes has been recently proved on a Portuguese coastal site, by means of innovative stable isotopes methodologies (Rascher et al, 2012). In general terms, the application of stable isotopes and geostatistical interpolation methods has been used at landscape, continental or global scales (isoscapes), to explicitly understand the spatial and temporally component of dynamic biological and chemical processes (West et al, 2008;Bowen et al, 2009a,b).…”

“…Such dynamics have striking environmental effects (Rascher et al, 2012) within the understory of the original mother plants, improving nutrient and water availability and reducing extreme temperatures and irradiances. In particular, the invasion process of A. cyclops appears to be favored by ageing or canopy decay.…”

Why so many flowers? A preliminary assessment of mixed pollination strategy enhancing sexual reproduction of the invasive <i>Acacia longifolia</i> in Portugal

“…Negative impacts have been recorded on native biodiversity (e.g. Hellmann et al, 2011;Marchante et al, 2003), ecosystem functioning and community structure (Rascher et al, 2011a(Rascher et al, , 2012Ulm et al, 2017). Even if literature exists on acacia flower characteristics and their reproductive conditions (reviewed by Stone et al, 2003, andby Kenrick, 2003), pollination and seed set are still poorly known for many species, especially in invaded areas.…”