October 16, 2013

By Kevin Merrill

The U.S. Department of Energy is supporting research by SNRE Professor Don Zak that may help finally answer how human production of nitrogen are shaping forests and the future of Earth’s climate.

The $1.4 million grant allows Zak and fellow researchers to continue studies and test new theories regarding how human-derived nitrogen deposited from the atmosphere and microbial communities within forest soils are working together. Zak’s efforts span nearly two decades and already have produced dozens scientific journal articles and led to new understandings about the role of forests, particularly northern forests, in global climate change. (Zak also holds a faculty appointment in the Department of Ecology and Evolutionary Biology in the College of Literature, Science, and the Arts.)

The funding comes from the DOE’s Office of Biological and Environmental Research. The office funds scientists working on research that examines Earth’s biogeochemical systems (atmosphere, land, oceans, sea ice, and subsurface) in determining climate.

The new efforts supported by this grant will look more deeply at changes already detected in microbial communities, specifically understand the genetic basis of how soil microorganisms respond to global change  Using genomic techniques, these researchers want to understand the molecular mechanisms by which atmospheric nitrogen deposition has reduced microbial decay and enhanced soil carbon storage in a forest ecosystem. The new experiments will increase understanding on whether a change in microbial community composition (who’s there and how many), function (what they are doing), or both underlie dramatic increases in the ability of soil to store carbon.

The research seeks to shed light on far-reaching global changes anticipated in the decades ahead. By the end of this century, Earth’s ecosystems will be bathed in quantities of nitrogen seen as unprecedented over the history of life on Earth, Zak said. This aspect of global change has the potential to limit the accumulation of anthropogenic (human-generated) carbon dioxide in the atmosphere, and therefore negatively affect the rate of climate warming.  For example, the amount of nitrogen entering terrestrial and aquatic ecosystems via non-anthropogenic sources (some nitrogen is made naturally, others in plants as part of the creation of fertilizer) is surpassed by nitrogen originating from fossil fuel combustion, biomass burning and the use of nitrogen-based chemical fertilizers.

In combination, these human-inspired processes have doubled the amount of biologically available nitrogen, a trend that is projected to increase over the next century.

Because these changes are concentrated in the Northern Hemisphere, forests in this region likely will be the future recipients of this additional human-derived nitrogen.  Collectively, these ecosystems already mediate important fluxes of carbon dioxide to and from the atmosphere and in doing so, compose a global “sink” that draws in and collects human-derived carbon dioxide. If nitrogen from human sources increases the speed and size of these global sinks (accelerates or grows the carbon cycle), then such a response could plausiblyslow the pace of climate warming by taking and absorbing more from the atmosphere

To date, Zak and his researchers have manipulated nitrogen deposition for 18 continuous years across in several northern forests.  It is thought to be the largest and longest-running experimental manipulation of atmospheric nitrogen deposition in any forest ecosystem worldwide. That experimental infrastructure is currently supported by a National Science Foundation grant that will sustain this experiment and maintain baseline data collection until 2018.

Over the course of a past grant that first began to study the microbial communities, Zak and his team have been able to involve two postdoctoral scholars, four doctoral students, four master’s students, and many undergraduate students.