Plant and soil nitrogen in oligotrophic boreal forest habitats with varying moss depths: does exclusion of large grazers matter?

• Published in: Oecologia
• Main Authors: Väisänen, Maria, Tuomi, Maria, Bailey, Hannah, Welker, Jeffrey M.
• Other Authors: UArctic Chairship, University of Oulu including Oulu University Hospital
• Format: Article in Journal/Newspaper
• Language: English
• Published: Springer Science and Business Media LLC 2021
• Subjects: Ecology, Evolution, Behavior and Systematics; Rangifer tarandus
• Online Access: http://dx.doi.org/10.1007/s00442-021-04957-0; https://link.springer.com/content/pdf/10.1007/s00442-021-04957-0.pdf; https://link.springer.com/article/10.1007/s00442-021-04957-0/fulltext.html

Abstract The boreal forest consists of drier sunlit and moister-shaded habitats with varying moss abundance. Mosses control vascular plant–soil interactions, yet they all can also be altered by grazers. We determined how 2 decades of reindeer ( Rangifer tarandus ) exclusion affect feather moss ( Pleurozium schreberi ) depth, and the accompanying soil N dynamics (total and dissolvable inorganic N, δ 15 N), plant foliar N, and stable isotopes (δ 15 N, δ 13 C) in two contrasting habitats of an oligotrophic Scots pine forest. The study species were pine seedling ( Pinus sylvestris L.), bilberry ( Vaccinium myrtillus L.), lingonberry ( V . vitis-idaea L.), and feather moss. Moss carpet was deeper in shaded than sunlit habitats and increased with grazer exclusion. Humus N content increased in the shade as did humus δ 15 N, which also increased due to exclusion in the sunlit habitats. Exclusion increased inorganic N concentration in the mineral soil. These soil responses were correlated with moss depth. Foliar chemistry varied due to habitat depending on species identity. Pine seedlings showed higher foliar N content and lower foliar δ 15 N in the shaded than in the sunlit habitats, while bilberry had both higher foliar N and δ 15 N in the shade. Thus, foliar δ 15 N values of co-existing species diverged in the shade indicating enhanced N partitioning. We conclude that despite strong grazing-induced shifts in mosses and subtler shifts in soil N, the N dynamics of vascular vegetation remain unchanged. These indicate that plant–soil interactions are resistant to shifts in grazing intensity, a pattern that appears to be common across boreal oligotrophic forests.