Effects of airborne ammonium and nitrate pollution strongly differ in peat bogs, but symbiotic nitrogen fixation remains unaffected

•N2 fixation of moss symbionts is not down-regulated by increased N deposition.•Ammonium N deposition leads to N stress response in keystone spp. of bogs.•Nitrate N deposition, in contrast, leads to increased peat N mineralization.•Differential N effects on bog ecosystem functioning should be taken into account. [Display omitted] Pristine bogs, peatlands in which vegetation is exclusively fed by rainwater (ombrotrophic), typically have a low atmospheric deposition of reactive nitrogen (N) (