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Nitrogen effects on decomposition: a five-year experiment in eight temperate sites.
1Department of Ecology, Evolution and Behavior, University of Minnesota, Saint Paul, Minnesota 55108, USA. shobbie@umn.edu
Ecology
|October 4, 2008
Summary
Nitrogen (N) addition did not inhibit lignin decomposition as expected. Instead, N slowed decomposition in sites with faster natural rates, potentially increasing carbon sequestration.
Area of Science:
- Ecology
- Biogeochemistry
- Soil Science
Background:
- Inorganic nitrogen (N) inputs impact decomposition, but effects on lignin-rich substrates are debated.
- Prior studies suggest N may inhibit lignin-degrading enzymes, but evidence is inconsistent.
Purpose of the Study:
- To investigate the effects of N addition on the decomposition of diverse substrates across grassland and forest sites.
- To test the hypothesis that N addition differentially affects decomposition based on initial substrate lignin concentration.
Main Methods:
- Studied decomposition of seven substrates with varying lignin content (7.4–25.6%) over five years.
- Conducted experiments across eight grassland and forest sites in Minnesota, USA.
- Assessed N addition effects on decomposition rates and lignin fraction decomposition.
Main Results:
- Nitrogen addition showed neutral or negative effects on overall decomposition rates.
- N's impact on decomposition was independent of initial substrate lignin concentration.
- Decomposition of the lignin fraction remained unaffected by N fertilization.
- Substrates with higher initial decomposition rates were more negatively impacted by N addition.
- N addition and low initial substrate N both stimulated N immobilization.
Conclusions:
- Decreased decomposition with N addition likely results from abiotic interactions or effects on the decomposer community, not enzyme inhibition.
- Atmospheric N deposition may enhance ecosystem carbon sequestration by reducing forest floor decomposition rates.
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