Open access publications in the SLU publication database

Abstract

The decomposition system is an important part of terrestrial ecosystems and as such regulated by several factors that are more or less well understood. One of the factors least understood is how decomposition is affected by increased nitrogen deposition. In view of the increased nitrogen deposition of large areas during the last 50 years and an interest in large-scale nitrogen fertilization of forests it has become important to better understand this factor. In this paper a short description of the decomposition system is given. I also did a literature review of published studies that have examined effects of added nitrogen on decomposition, especially effects on mass loss, microbial respiration, microbial biomass and extracellular enzyme activity. The reported results are conflicting. Overall, the most frequent observation was a zero-effect of nitrogen addition and a smaller, but almost equal, number of reports demonstrated increasing and decreasing rates of decomposition. I have tried to identify factors that could have interacted with the added nitrogen and caused the variability in effects. Possible interacting factors were: climate, nitrogen source, level of ambient nitrogen deposition, length of measurement period, frequency of nitrogen application, availability of other nutrients, litter quality and change in decomposer properties. The most likely candidate explaining the diverging results seems to be the length of the observation period and if the substrate was litter or soil organic matter. Decomposition over short periods of litter was generally stimulated by nitrogen addition whereas the respiration from soil organic matter rather decreased.