Potential NH₄ ⁺ and NO₃ ^- uptake in seven Sphagnum species

The rate of nitrogen uptake by seven Sphagnum species, which from a gradient from hummock to hollow and from ombrotrophic to minerotrophic conditions, was measured as the decrease in the concentrations of NH₄ ⁺ and NO₃ ^- from solutions in which capitula were grown under laboratory conditions. The highest uptake rate was by individuals of each species with large capitula and a high number of ion exchange sites, i.e. lawn species (S. pulchrum, S. fallax, S. papillosum and S. magellanicum). On a dry-mass basis, the most effective species were the hummock species (S. fuscum and S. rubellum), even though these species have a low dry mass. Hummock species, which occur in high densities and have high potential N-uptake rates on a dry-mass basis, were the most effective species in retaining available nitrogen.