Exposure to nitrogen does not eliminate N2 fixation in the feather moss Pleurozium schreberi (Brid.) Mitt.

Background and aims

The feather moss Pleurozium schreberi (Brid.) Mitt. is colonized by cyanobacteria, which fix substantial amounts of atmospheric nitrogen (N) in pristine and N-poor ecosystems. Cyanobacterial N₂ fixation is inhibited by N deposition. However, the threshold of N input that leads to the inhibition of N₂ fixation has not been adequately investigated. Further, the ability of N₂ fixation to recover in mosses from high N deposition areas has not been studied to date.

Methods

We conducted two laboratory studies in which we (1) applied a range of concentrations of N as NH₄NO₃ to mosses from low N-deposition areas, and (2) we deprived mosses from a high N-deposition area of N to test their ability to recover N₂ fixation.

Results

Higher addition rates (up to 10 kg N ha^?1) did not systematically inhibit N₂ fixation in P. schreberi. Conversely, upon weeks of N deprivation of mosses from a high N environment, N₂ fixation rates increased.

Conclusions

The threshold of total N deposition above which N₂ fixation in P. schreberi is inhibited is likely to be > 10 kg N ha^?1. Further, cyanobacteria are able to recover from high N inputs and are able to fix atmospheric N₂ after a period of N deprivation.