The Sensitivity of Moss-Associated Nitrogen Fixation towards Repeated Nitrogen Input
Kathrin Rousk1,2, Anders Michelsen1,2
1Department of Biology, Terrestrial Ecology Section, University of Copenhagen, Universitetsparken 15, DK-2100, Copenhagen, Denmark.
Plos One
|January 6, 2016
Summary
Nitrogen fixation by cyanobacteria in feather mosses can be inhibited by high nitrogen (N) input. However, sensitivity to repeated N additions may decrease if N input stays below a certain threshold, allowing for ecosystem N gains.
Area of Science:
- Ecology
- Environmental Science
- Microbiology
Background:
- Nitrogen (N2) fixation is crucial for N-limited ecosystems like boreal forests and subarctic tundra.
- Feather mosses, such as Hylocomium splendens, host N2-fixing cyanobacteria, potentially increasing ecosystem nitrogen pools.
- Nitrogen input is known to inhibit N2 fixation in mosses, but tolerance to repeated N additions is unclear.
Purpose of the Study:
- To investigate the recovery and changing sensitivity of N2 fixation in H. splendens under varying nitrogen loads.
- To determine if repeated nitrogen additions decrease the sensitivity of N2 fixation.
- To assess nitrogen retention capabilities of mosses at different N input levels.
Main Methods:
- Experimentally applying different nitrogen loads (0, 5, 20, 80, 320 kg N ha(-1) yr(-1)) to H. splendens.
- Measuring N2 fixation rates after a period of N deprivation and during repeated N additions.
- Analyzing nitrogen recovery in leachate to assess moss retention.
Main Results:
- High N addition (320 kg N ha(-1) yr(-1)) inhibited N2 fixation, while a low addition (5 kg N ha(-1) yr(-1)) promoted it.
- N2 fixation increased during a brief period of N deprivation across all treatments.
- Sensitivity to repeated N additions decreased at 20 and 80 kg N ha(-1) yr(-1) but increased at 320 kg N ha(-1) yr(-1).
- Nitrogen recovery in leachate increased with N load, indicating poor retention above 5 kg N ha(-1) yr(-1).
Conclusions:
- Moss N2 fixation exhibits reduced sensitivity to repeated N additions below a specific threshold.
- Ecosystem nitrogen gains from moss N2 fixation are possible but depend on nitrogen input levels.
- Mosses have limited nitrogen retention capacity when N input exceeds 5 kg N ha(-1) yr(-1).
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