Explanation to data of "Potential contributions of root decomposition to the nitrogen cycle in arctic forest and tundra", by Sabrina Träger, Ann Milbau & Scott D. Wilson, Ecology and Evolution. Data file "Root_Ncycling.xlsx". 1. Sheet "root length" Presented are data of root length (in mm) at a specific sampling time (e.g. 13/06/2013). Root length is given for roots of a specific diameter and color class per plot per habitat. Habitats: forest or tundra. Color class: W - white or B - brown. Diameter class: 0.1 - <0.1 mm; 0.2 - 0.1-0.2 mm; 0.5 - 0.2-0.5 mm; 1 - 0.5-1 mm; 2 - 1-2 mm. 2. Sheet "SRL" Presented are data needed specific root length (SRL) calculations. Habitats: forest or tundra. Color class: W - white or B - brown. Diameter class: 0.1 - <0.1 mm; 0.2 - 0.1-0.2 mm; 0.5 - 0.2-0.5 mm; 1 - 0.5-1 mm; 2 - 1-2 mm. Length of a specific root is given in cm, weight of a specific root is given in mg. 3. Sheet "root_N-c" Presented are data of root nitrogen (N), carbon (C) concentrations, and C/N ratio for roots within a specific habitat of a specific color and diameter class, sampled in 2013. Habitats: forest or tundra. Color class: W - white or B - brown. Diameter class: 0.1 - <0.1 mm; 0.2 - 0.1-0.2 mm; 0.5 - 0.2-0.5 mm; 1 - 0.5-1 mm; 2 - 1-2 mm. N and C are shown in percentage. nt - not tested. 4. Sheet "aboveground_biomass_&_N-c" Presented are data of aboveground biomass and nitrogen (N), carbon (C) concentrations, and C/N ratio, with aboveground vegetation being separated in different types, sampled in 2013 and 2014. Habitats: forest or tundra. Types: U - forest understorey; L - forest leaves; T - forest twigs; A - tundra aboveground vegetation. Biomass is given in g/m^2. N and C are shown in percentage. nt - not tested. 5. Sheet "decomp_roots_N-c" Presented are data of root nitrogen (N), carbon (C) concentrations, and C/N ratio for roots before decomposition (intial) and after decomposition depending where they decomposed (home or away), within a specific habitat of a specific diameter class. Habitats: forest or tundra. Site-plot combinations include information about the site (L,N,S), elevation, plot number, and for after-decomposition samples sample name (S1/S2 and B1/B2). Root classes: S - <0.2 mm; B - >0.2 mm. Decomp(osition)type: I - initial (before decomposition); H - home decomposition (decomposed in the home habitat); A - away decomposition (decomposed in the away habitat). N and C are shown in percentage. 6. Sheet "decomp_roots_weight" Presented are data of root weight before decomposition (air dried), within a specific habitat of a specific diameter class. Habitats: forest or tundra. Site-plot combinations include information about the site (L,N,S), elevation, and plot number. Root classes: S - <0.2 mm; B - >0.2 mm. Decomp(osition)type: H - home decomposition (decomposed in the home habitat); A - away decomposition (decomposed in the away habitat). Biomass is given in g, measured before decomposition. 7. Sheet "decomp_aboveground_N-c" Presented are data of aboveground tissue nitrogen (N), carbon (C) concentrations, and C/N ratio for aboveground tissue before decomposition (intial) and after decomposition depending where they decomposed (home or away), within a specific habitat. Habitats: forest or tundra. Site-plot combinations include information about the site (L,N,S), elevation, and plot number. Type: L - leaves. Decomp(osition)type: I - initial (before decomposition); H - home decomposition (decomposed in the home habitat); A - away decomposition (decomposed in the away habitat). N and C are shown in percentage. 8. Sheet "decomp_aboveground_weight" Presented are data of aboveground tissue weight before decomposition (air dried), within a specific habitat. Habitats: forest or tundra. Site-plot combinations include information about the site (L,N,S), elevation, and plot number. Decomp(osition)type: H - home decomposition (decomposed in the home habitat); A - away decomposition (decomposed in the away habitat). Biomass is given in g, measured before decomposition.