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 Projects:
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.

Selected Publications:

Zak, D.R., W.E. Holmes, A.C. Finzi, R.J. Norby, and W.H. Schlesinger. 2003. Soil nitrogen cycling under elevated CO2: a synthesis of forest FACE experiments. Ecological Applications 13: 1051-1061.

DeForest, J.L., D.R. Zak, K.S. Pregitzer, and A.J. Burton. 2004. Experimental NO3- additions alter microbial community function in northern hardwood forests. Soil Science Society of America Journal 68: 132-138.

Pregitzer, K.S., D.R. Zak, A.J. Burton, and J.A. Ashby. 2004. Chronic nitrate additions dramatically increase the export of carbon and nitrogen in northern hardwood forests. Biogeochemistry 68: 179-197.

Zak, D.R., K.S. Pregitzer, W.E. Holmes, A.J. Burton and G.P. Zogg. 2004. Anthropogenic N deposition and the fate of 15nitrate in a northern hardwood ecosystem. Biogeochemistry 69: 143-157.

DeForest, J.L., D.R. Zak, K.S. Pregitzer, and A.J. Burton. 2004. Nitrate deposition and the microbial degradation of cellulose and lignin in a northern hardwood forest. Soil Biology & Biochemistry 36: 965-971.

Waldrop, M.P., D.R. Zak, and R.L. Sinsabaugh. 2004. Microbial community response to nitrogen deposition in northern forest ecosystems. Soil Biology & Biochemistry 36: 1443?1451.

Sinsabaugh, R.L., D.R. Zak, M. Gallo, C. Lauber, and A. Amonette. 2004. Nitrogen deposition and dissolved organic carbon production in northern temperate forests. Soil Biology & Biochemistry 36:1509-1515.

Waldrop, M.P., D.R. Zak, R.L. Sinsabaugh, M. Gallo, and C. Lauber. 2004. Nitrogen deposition modifies soil carbon storage through changes in microbial enzyme activity. Ecological Applications 14: 1172-1177.

Hassett, J.E., and D.R. Zak. 2005. Aspen harvest intensity decreases microbial biomass, extracellular enzyme activity and soil nitrogen cycling. Soil Science Society of America Journal 69: 227-235.