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Study Shows Limited Nitrogen Curbs Plants' Ability to Absorb Carbon Dioxide

RELEASED: April 13, 2006

Tali Lee
Tali Lee

EAU CLAIRE — University of Wisconsin-Eau Claire ecophysiologist Tali Lee is among the authors of a study published this week in the prestigious journal Nature.

The study, led by Peter B. Reich, department of forest resources, University of Minnesota, showed that plants may not be as effective at removing increasing amounts of carbon dioxide from the atmosphere and tempering global warming as had been hoped.

Although plants in the study initially increased their growth when exposed to elevated CO2, they eventually became limited by the amount of nitrogen available to them in the surrounding soil.

Lee, who started working with Reich at Minnesota before joining the UW-Eau Claire biology department faculty in 2002, said plants have been expected to offset some of the rise in global CO2 levels by taking up the greenhouse gas in the process of photosynthesis and incorporating the carbon into new growth. However, it has been a matter of some debate whether the availability of nitrogen, which is also vital for plant growth, could limit this process.

In one of the longest-running studies to tackle this question, Reich and his colleagues, including Lee, show that the stimulation in growth of several grassland species induced by experimentally elevated CO2 becomes restricted at normal levels of soil nitrogen after only four to six years. The same species continue to grow at elevated rates if their soil is enriched with additional nitrogen.

"In the first two years, the increase in plant growth due to elevated CO2 did not depend on the amount of nitrogen in the soil," Lee said. "But by years four to six, elevated CO2-induced increase in plant growth was less under normal compared to enriched nitrogen levels."

Lee and her colleagues say it will be important to understand the variability in nitrogen availability worldwide in order to accurately estimate the role of vegetation as a future carbon sink.

"Future models will need to pay attention to this idea that plants won't necessarily continue to be carbon sinks," Lee said. "It's important to understand the role of nitrogen in vegetation responses to global change and how that varies over time."

Support for the research study came from the U.S. Department of Energy Program for Ecosystem Research, the National Science Foundation Long-Term Ecological Research and Biocomplexity Coupled Biogeochemical Cycles Programs and the University of Minnesota.

The study is Lee's third publication to be accepted into Nature, which along with the journal Science, is where much of the current and cutting edge contributions to science are published, said department chair Paula Kleintjes.

"It is quite an honor and accomplishment for Dr. Lee and her colleagues to have their work recognized and widely read by such an international audience," Kleintjes said. "We are extremely proud of her as she continues to sustain excellence as an accomplished scientist and exceptional teacher at UW-Eau Claire."

Kleintjes describes Lee as an engaging professor who not only shares her expertise on plant structure and function in the classroom, but who also serves as a wonderful mentor and collaborator for many of the undergraduate research students in her lab.

Lee said three UW-Eau Claire students who have since graduated — Kalli Worm, Emily Hockman and Lauren Losek — worked as summer research interns during the study. Claire Mickelson, a junior from Maple Grove, Minn., will be a research intern this summer.

"The students are involved in collecting biomass, measuring rates of photosynthesis and recording data," Lee said. "It's an opportunity for them to make scientific inquiry a real experience and helps bring their understanding of science and confidence in their abilities to the next level."

Lee holds a bachelor of science degree in biology and mathematics from Grand Canyon University and a Ph.D. in plant biological sciences from the University of Minnesota-Twin Cities, where she also completed a postdoctoral program. She teaches Plant Form and Function and Plant Physiology. Her research interests include the physiological and growth responses of plants to changing environmental conditions.

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JW/JB

CONTACT:

Tali Lee, University of Wisconsin-Eau Claire, (715) 836-4415, E-mail: leetd@uwec.edu.

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