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. 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:
From Genes to ecosystems: mechanisms controlling long-term ecosystem response to nitrogen deposition. Sponsor: NSF Ecosystem Science Program

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 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

Selected Publications:

Sefcik, L.T., D.R. Zak and D.S. Ellsworth. 2007. Seedling survival is increased by elevated atmospheric CO₂. Global Change Biology 13: 132-146.

Blackwood, C.B., M.P. Waldrop, D.R. Zak and R.L. Sinsabaugh. 2007. Molecular analysis of fungal communities and laccase genes in decomposing litter reveal differences among forest types but no impact of N deposition. Environmental Microbiology 9: 1306-1316.

Chung, H., D.R. Zak, D.S. Ellwsorth, and P.B. Reich. 2007. Plant diversity, elevated CO₂ and atmospheric N deposition alter microbial community composition and function. Global Change Biology 13: 980-989.

Allison, V.J., T.K. Rajaniemi, D.E. Goldberg, and D.R. Zak. 2007. Quantifying direct and indirect effects of fungicide on an old-field plant community: an experimental null-community approach. Plant Ecology 190: 53-69.

Blackwood, C.B., D.E. Hudleston, D.R. Zak and J.S. Buyer. 2007. Interpreting ecological diversity indices applied to T-RFLP data: insights from simulated microbial communities. Applied and Environmental Microbiology 73: 5276-5283.

Zak, D.R., W.E. Holmes, K.S. Pregitzer, J.S. King, D.S. Ellsworth, and M.E. Kubiske. 2007. Belowground composition and the response of developing forest communities to atmospheric CO₂ and O₃. Global Change Biology 13: 2230-2238.

Finzi, A.C., R.J. Norby, C. Calfapietrac, A. Gallet-Budyneka, B. Gielend, W.E. Holmes, M.R. Hoosbeek, C.M. Iversen, R.B. Jackson, M.E. Kubiske, J. Ledford, M. Liberloo, R. Oren, A. Polle, S. Pritchard, D.R. Zak, and R. Ceulemans. 2007. Increases in nitrogen uptake rather than nitrogen-use efficiency support high rates of temperate forest productivity under elevated CO₂. Proceeding of the National Academy of Sciences 104: 14014-14019.

Smemo, K.A., D.R. Zak, K.S. Pregitzer, and A.J. Burton. 2007. Characteristics of DOC exports from northern hardwood forests receiving chronic atmospheric NO₃^- deposition. Ecosystems 10: 369-379.

Zak, D.R., W.E. Holmes, and K.S. Pregitzer. 2007. Atmospheric CO₂ and O₃ alter the flow of ¹⁵N in developing forest ecosystems. Ecology 88: 2630-2639.

Blackwood, C.B., D.R. Zak and J.S. Buyer. 2007. Tilting at windmills: a response to a recent critique of terminal restriction fragment length polymorphism data - Reply. Appl. Environ. Microbiol. 73: 8141-8042.

Homockel, K.S., D.R. Zak and C.B. Blackwood. 2007 Does atmospheric N deposition alter the abundance and activity of lignolytic fungi in forest soils? Ecosystems 10: 1278-1286.

Pregitzer, K.S., A.J. Burton, D.R. Zak, and A.F. Talhelm. 2008. Simulated chronic N deposition increases carbon storage in northern temperate forests. Global Change Biology 14: 142–153.

Lesaulnier, C., D. Papamichail, S. McCorkle, B. Ollivier, S. Skiena, S. Taghavi, D.R. Zak, and D. van der Lelie. 2008. Elevated CO₂ affects soil microbial diversity associated with trembling aspen. Environmental Microbiology 10: 926-941.

Eddy, W.E., D.R. Zak, W.E. Holmes, and K.S. Pregitzer. 2008. Chronic NO₃^- deposition does not induce NO₃^- use by Acer saccharum Marsh. Ecosystems 11: 469-477.