Increased Nitrogen Deposition Slows Carbon Decomposition in Forest Soils

The Science

Global production of agricultural fertilizers has vastly increased the amount of nitrogen compounds entering natural terrestrial ecosystems. Although it is clear that increased nitrogen availability boosts primary productivity (i.e., plant growth) in ecosystems, the impacts of this nitrogen influx on the decomposition of dead plant material by soil microbes remain poorly understood. A collaborative team of U.S. Department of Energy researchers at the Universities of Michigan and Oklahoma examined carbon decomposition by soil fungi and bacteria at an experimental forest site in Michigan. GeoChip 4.0, a DNA microarray containing probes for thousands of functional genes, was used to measure expression of genes involved in degradation of complex carbon compounds in soil samples from sites that have been exposed to elevated nitrogen input for the past 18 years. Compared to nearby control plots, sites with elevated nitrogen showed significant decreases in the diversity and overall expression levels of fungal and actinobacterial genes involved in deconstruction of cellulose, lignin, and other plant compounds. This finding correlates with a long-term observation of decreased carbon decomposition rates in soils at the nitrogen-elevated sites and points to the specific mechanism underlying this shift. These findings shed new light on poorly understood processes occurring in forest soils and improve our ability to better predict how ecosystems will respond to changing environmental variables.

The Impact

The compositions of genes encoding oxidoreductases, which plausibly mediate lignin decay, were responsible for much of the observed dissimilarity between actinobacterial communities under ambient and experimental N deposition. This shift in composition and decrease in richness and diversity of genes encoding enzymes that mediate the decay process has occurred in parallel with a reduction in the extent of decay and accumulation of soil organic matter. These observations indicate that compositional changes in actinobacterial and fungal communities elicited by experimental N deposition have functional implications for the cycling and storage of carbon in forest ecosystems. This study revealed that even small changes in community composition (25% difference in fungi; 18% in actinobacteria) could lead to important biogeochemical implications.

BER Program Manager

Dawn Adin

U.S. Department of Energy, Biological and Environmental Research (SC-33)
Biological Systems Science Division
[email protected]


Eisenlord, S. D., Z. Freedman, D. R. Zak, K. Xue, Z. He, and J. Zhou. 2013. “Microbial Mechanisms Mediating
Increased Soil Carbon Storage under Elevated Atmospheric Nitrogen Deposition,” Applied Environmental Microbiology 79, 1191–99. DOI: 10.1128/AEM.03156-12.