Trees out‐forage understorey shrubs for nitrogen patches in a subarctic mountain birch forest

Nitrogen (N), acquired by roots and mycorrhizal fungi supplied to plant foliage, is a growth-limiting nutrient at the subarctic treeline. Due this limitation, interspecific competition acquisition of N an important control on community composition distribution. The ability trees shrubs access shapes dynamics ecotone undergoing species range shifts changes in primary productivity driven climate change. Using 15N soil labelling we investigate fate inorganic N, spatial distances over which understorey treeline forest. was injected into rooting zones discrete 1 m2 patches foliar samples were collected from between 50 m away, 0.5 11 away labelled soil. label found mountain birch up 5 m, 2 We estimate that 1.27% pulse-derived foliage trees, compared 1.16% understorey. However, contributed only 31% ecosystem leaf area index (LAI), thus there disproportionate allocation added canopy with its contribution LAI. difference root exploration partitioning may confer competitive advantage respect nitrogen patches, alter structures within these forests. This particularly considering predicted climate-driven tree tall shrub expansion regions, likely consequences for carbon (C) cycling, as well biodiversity.