The University of Montana
College of Forestry and Conservation
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The Global N Cycle

Human activities have driven profound Niwotchanges to the global nitrogen (N) cycle, with estimates indicating that anthropogenic activities like food and energy production have roughly doubled the annual N added to terrestrial ecosystems via natural processes. The benefits of anthropogenic N are obvious; it fueled the Green Revolution, and food produced with N fertilizer feeds billions of people across the planet. However, anthropogenic N inputs also have a range of undesired ecological effects, and I am interested in understanding how increases in environmental N availability affect both humans and the ecosystems we depend on. I collaborate with several groups on a range of projects, including plot-level estimates of the effects of N deposition on soil and plant processes and diversity, analyses of the effects of salmon-derived nutrients on ecosystem processes, and global-scale estimates of the effects of N on human health, among others.

In addition, while it is unquestionable that humans have sharply increased the rate at which atmospheric N is fixed into reactive forms, comparisons between anthropogenic and natural inputs are only tenuous at best. Biological nitrogen fixation (BNF) provides the largest source of “new” N to natural ecosystems, and therefore estimates of the degree to which the N cycle has been perturbed require a thorough understanding of N inputs via BNF. However, for a number of reasons, both small- and large-scale rates of N fixation in natural ecosystems are very poorly constrained. Thus, I am interested in understanding the biotic and abiotic controls over free-living N fixation, and am using a suite of experimental manipulations to address this question. With scientists at the University of Colorado, I am investigating how nutrient availability regulates N fixation in both soils and in the canopies of tropical rain forests. N fixation rate estimates are now being augmented with detailed genetic (nifH) characterizations of the N-fixer community to determine what regulates the abundance and diversity of N fixing organisms, and how microbial community composition influences N fixation rates.

Finally, I am a member of the International Nitrogen Initiative (INI), an international scientific organization focused on understanding the global N cycle, how it is changing, and how our science may best be used to inform policy that could help mitigate the negative effects of N enrichment in the environment. Within the INI, I am leading an effort to improve estimates of N fixation in natural ecosystems using a “top-down” strategy that includes a modeling and an ecosystem N balance approach. This effort involves collaborators from the University of Colorado, the University of California Davis, Brazil and the UK.


For questions about the research we do, or for information about opportunities in the lab, please contact me directly.

Cory Cleveland, Associate Professor
Department of Ecosystem & Conservation Sciences
College of Forestry & Conservation
CHCB 423/32 Campus Drive
University of Montana
Missoula, MT 59812

Phone: 406-243-6018 | Fax: 406-243-6656
Email: |