Don Zak holds a joint appointment in the department of Ecology and Evolutionary Biology, College of Literature, Science, and Arts. His research investigates links between the composition and function of soil microbial communities and the influence of microbial activity on ecosystem-level processes. This work draws on ecology, microbiology, and biochemistry and is focused at several scales of understanding, ranging from the molecular to the ecosystem scale. Current research centers on understanding the link between plant and microbial activity within terrestrial ecosystems, and the influence climate change may have on these dynamics. Teaching includes courses in soil ecology and ecosystem ecology.

Awards and Grants:
Atmospheric nitrogen deposition and molecular mechanisms enhancing soil carbon storage. Sponsor: DoE Biological and Environmental Research

Ecosystem response to elevated CO₂ and O₃ is controlled by plant-microbe interactions in soil. Sponsor: DoE Program for Ecosystem Research

Long-term ecosystem response to chronic atmospheric nitrogen deposition. Sponsor: NSF Long-Term Research in Environmental Biology Program (LTREB)

Research Interests:
My research investigates connections between microbial community composition and function and the importance of microbial activity in regulating ecosystem-level processes. This work draws on microbial ecology and plant physiology, and it is focused at several scales of understanding. Plants respond to environmental factors by altering growth and longevity of fine roots, which, in part, control the amount and types of organic substrates available for microbial metabolism in soil. I have worked to understand how changes in belowground plant growth influence the composition and function of soil microbial communities. Stable isotopes and molecular techniques are the primary tools I have used to accomplish this task. My work has elucidated mechanisms of plant-microbe competition for inorganic nitrogen and the interdependence of plant and microbial productivity in a wide range of terrestrial ecosystems. Much of my current work centers on understanding the link between plant and microbial activity within terrestrial ecosystems, and the influence climate change may have on these dynamics.

Current/Recent Research:
Elevated Atmospheric CO₂ and Feedback between Carbon and Nitrogen Cycles: The physiological response of plants to atmospheric CO₂ has received considerable attention because CO₂ is the substrate for photosynthesis and its atmospheric concentration is likely to double in the next century. Although the extent and duration over which such an increase might occur is debatable, it is likely to have important consequences for the rate at which organic matter and associated plant nutrients are cycled within terrestrial ecosystems. We tested a conceptual model depicting the influence of elevated atmospheric CO₂ on plant production, soil microorganisms, and the rate at which C and N are cycled within the plant-soil system. The model is based on the premise that above and below-ground plant production provide the primary link between the rising atmospheric CO₂ concentration and changes in the cycling of C and N within terrestrial ecosystems. Our data support the hypothesis that, at least for one growing season, increased root growth can elicit a positive feedback response by microbial populations and N dynamics within the soil.

Teaching Interests:
My teaching builds an understanding of the processes controlling the flow of energy and nutrients within terrestrial ecosystems and how these dynamics are altered by human activity. I accomplish this through a series of undergraduate and graduate courses that focus on microbial ecology and ecosystem ecology. In Soil Ecology (NRE 430/BIO 498), I provide students with the fundamental principles of soil science, stressing the integration of concepts into an understanding of ecosystem-level processes. I complement formal lectures with informal teaching in field and laboratory settings, an approach that has been useful for putting concepts and theory into action. Ecosystem Ecology (NRE 476/BIO 476) is a lecture course that focuses on understanding the physical, chemical and biochemical processes regulating the dynamics of terrestrial and aquatic ecosystems; it is team taught by myself and Dr. George Kling. We discuss classic and current topics in ecology that have built our understanding of ecosystem organization and function. Some aspects of population and community ecology are presented to gain an in-depth understanding of how and why ecosystems change in time and space. The course integrates across disciplines of physiological, population, and community ecology to understand how and why ecosystems differ in composition, structure, and function. Students are expected to have a solid background in biology and ecology. We also expect that students will be able to use principles of mathematics, physics, chemistry and biology as tools to understand ecological processes occurring at the ecosystem level.

Current/Recent Teaching:
General Ecology – BIO/ENVIRON 281
Soil Ecology – EEB 489/ENVIRON 430
Ecosystem Ecology – EEB/ENVIRON 476
Ecosystem Science in the Rocky Mountains - GEOLOGY/ENVIRON 341

Recent Publications:

Edwards, I.P., and D.R. Zak 2011.  Fungal community composition and function after long-term exposure of northern forests to elevated atmospheric CO₂ and O₃. Global Change Biology 17: 2184-2195.

Pregitzer, K.S., D.R. Zak, A. Talhelm, A.J. Burton, and J. Eikenberry. 2011. Nitrogen turnover in the leaf litter and fine roots of sugar maple. Ecology 91: 3456-3462.

Fornara D.A., R. Bardgett, S. Steinbeiss, D. R. Zak, G. Gleixner, and D. Tilman 2011. Plant effects on soil N mineralization are mediated by the composition of multiple soil organic fractions. Ecological Research 26: 201-208.

Hofmockel, K.S., D.R. Zak, and J.D. Jastrow. 2011. Change in forest soil organic matter pools after a decade of elevated CO₂ and O₃. Soil Biology & Biochemistry 43: 1518-1527.

Edwards, I.P., D.R. Zak, H. Kellner, S.D. Eisenlord and K.S. Pregitzer. 2011. Simulated atmospheric N deposition alters fungal community composition and suppresses lignocellulolytic gene expression in forest floor of a northern hardwood forest. PLoS One 6:e20421.

Weber, C.F., D.R. Zak, B.A. Hungate, R.B. Jackson, R. Vilgalys, R.D. Evans, C.W. Schadt, J.P. Megonigal, and C.R. Kuske. 2011. Responses of soil cellulolytic fungal communities to elevated atmospheric CO₂ are complex and variable across five ecosystems. Environmental Microbiology doi:10.1111/j.1462-2920.2011.02548.x

Zak D.R., K.S. Pregitzer, A.J. Burton, I.P. Edwards, and H. Kellner. 2011. Microbial responses to a changing environment: implications for the future functioning of terrestrial ecosystems. Fungal Ecology 4: 386-395.

Zak, D.R., K.S. Pregitzer, M.E. Kubiske, and A.J. Burton. 2011.  Forest productivity under elevated CO₂ and O₃: positive feedbacks to soil N cycling sustain decade-long net primary productivity enhancement by CO₂. Ecology Letters doi: 10.1111/j.1461-0248.2011.01692.x.

Norby, R.J., and D.R. Zak. 2011. Ecological lessons from free-air CO₂ enrichment (FACE) experiments. Annual Review of Ecology, Evolution & Systematics. 42:181–203.

Talhelm, A.F., K.S. Pregitzer, A.J. Burton and D.R. Zak. 2011. Air pollution and the changing biogeochemistry of northern forests. Frontiers in Ecology and the Environment doi:10.1890/110007

Burton, A.J., Jarvey, J.C., Jarvi M.P., D.R. Zak, and K.S. Pregitzer. 2011. Chronic N deposition alters root respiration: tissue N relationships in northern hardwood forests. Global Change Biology doi: 10.1111/j.1365-2486.2011.02527.x.

Patterson, S.L., D.R. Zak, A.J. Burton, A.F. Talhelm, and K.S. Pregitzer. 2011. Simulated N deposition negatively impacts sugar maple regeneration in a northern hardwood ecosystem. Journal of Applied Ecology doi: 10.1111/j.1365-2664.2011.02090.x

Zak, D.R., M.E. Kubiske, K.S. Pregitzer, and A.J. Burton. 2012. Atmospheric CO₂ and O₃ alter competition for soil nitrogen in developing forests. Global Change Biology 18: 1480-1488.

Dunbar, D., S.A. Eichorst, L. Gallegos-Graves, S. Silva, G, Xie, D. Evans, D.A. Hungate, R.B. Jackson, J.P. Megonigal, C.W. Schadt, R. Vilgalys, D.R. Zak, and C.R. Kuske. 2012. Common bacterial responses in six ecosystems explosed to ten years of elevated atmospheric carbon dioxide. Environmental Microbiology doi:10.1111/j.1462-2920.2011.02695.x

Whittinghill, K.A., W.S. Currie, D.R. Zak, A.J. Burton, and K.S. Pregitzer. 2012. Anthropogenic N deposition increases soil C storage by decreasing the extent of litter decay: analysis of field observations with a biogeochemical model. Ecosystems doi: 10.1007/s10021-012-9521-7

Eisenlord, S.D., D.R. Zak and R.A. Upchurch. 2012. Dispersal limitation and the assembly of soil Actoinobacteria communities in a long-term chronosequence. Ecology and Evolution doi: 10.1002/ece3.210