Thyme travels: 15 N isoscapes of T hymus vulgaris   L . invasion in lightly grazed pastoral communities

Alterations to ecosystem nitrogen ( N ) cycling by introduced plant species may increase the invasibility of habitat providing a positive feedback for the introduced species to become invasive. Spatial patterns of foliar and soil δ 15 N ratios reflect variation in rates and process of N ‐cycling across invaded landscapes and provide insight into N ‐source uptake and utilization strategies of invasive plant species. To evaluate invasion‐associated changes in soil and foliar δ 15 N at different scales: regional (among different sites), local (between north‐ and south‐facing aspect at the same site), and microsite (within populations in the same community), we measured foliar and soil δ 15 N , animal faeces cover (as a proxy for grazing intensity) and N 2 ‐fixing species cover from inside to outside T hymus vulgaris L . (thyme)‐invaded lightly grazed pastoral communities in C entral O tago, southern S outh I sland, N ew Z ealand. Mean thyme foliar δ 15 N were near‐zero across the invaded landscape, and did not change across the advancing edge of invasion or with aspect. There was no evidence that associations with N 2 ‐fixing species provide a potential N source. Soil δ 15 N was lower inside of thyme compared to at the edge or outside of thyme and was varied between aspects at some sites. Animal faeces cover as a proxy for grazing intensity explained only 23% of this observed variation of soil δ 15 N . Thyme invasion may result in lowered soil δ 15 N reflecting alterations to N dynamics. Associated invasion‐related impacts of animal grazing may also impact soil δ 15 N . Further studies are required to distinguish the underlying mechanism responsible for the observed patterns of foliar and soil δ 15 N values across thyme‐invaded C entral O tago landscapes.