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Updated 12:30 PM February 14, 2007




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Plant decay findings informresponse to climate change

A study by a team of scientists from the School of Natural Resources and Environment (SNRE) and four other major universities sheds new light on the factors that affect how a key plant and soil nutrient, nitrogen, is released during the decay of dead plant tissue and other organic matter in soils.

The findings from their decade-long global study, which appeared in a recent issue of Science, are likely to make a strong contribution to the improvement of ecosystem models. This ultimately may help scientists increase their ability to predict how ecosystems respond to and mediate aspects of global change, including global climate change.

The decomposition of leaf and root debris, or plant "litter," is a lengthy process that converts the products of photosynthesis to inorganic components and stable soil organic matter. In terrestrial ecosystems, it represents the primary source of nutrients, particularly nitrogen, needed for plant growth, and provides both nutrients and energy for microbes that live in the soil. In addition to nitrogen, however, decomposition also releases more carbon annually than fossil-fuel combustion, which over time may have a serious impact on the environment.

"Until now, the lack of long-term, broad-scale studies on litter decomposition and nutrient release has prevented us from making accurate predictions about ecosystem carbon balance and response to environmental change on regional and global scales," says William Currie, an associate professor at SNRE, who collaborated on the project. "Gaining a better understanding of the controls on net nitrogen release during decay will greatly improve our ability to predict terrestrial carbon dynamics."

The Long-Term Intersite Decomposition Experiment (LIDET) used data collected from several leaf and root litter samples that differed in chemical quality. More than 10,000 of these samples were carefully tagged and distributed around 21 field sites that ranged geographically from the Arctic to the Antarctic and encompassed all types of ecosystems in between, including forests, deserts, grasslands and the humid tropics.

The decomposing leaves and roots were monitored over a 10-year period by numerous investigators and students from dozens of institutions. The project's goal was to determine which combination of climate and initial litter-chemistry variables best predicted the long-term patterns in the release of nitrogen.

Nitrogen is a key nutrient studied by ecosystem scientists because it is needed by all plants and animals and strongly controls plant growth and plant nutrition for animals. Since nitrogen is typically in short supply, its release from decaying plant tissues controls the availability of this nutrient for the growth of the next generation of plants.

"The processes of growth and decay continue in each generation, cycling the nitrogen from living to dead and back to living plants," Currie explains. "Because of the key role nitrogen plays in photosynthesis, this cycling ultimately controls the storage of carbon from the atmosphere."

The research team found that the amount of nitrogen released largely was determined by the initial concentration of nitrogen present in leaf litter and the mass of litter remaining. "Contrary to previous beliefs, this pattern holds true globally, regardless of climate, other litter chemical properties, soil conditions or soil microbial communities," Currie says.

The scientists also reported that the rate of leaf and root litter decomposition was affected by temperature and moisture, with cold, dry regions showing the slowest rates and warm, moist tropical forests the fastest. The only exception was the rapid decomposition rate they observed in arid-zone grasslands, which may have been affected by ultraviolet radiation in addition to climate.

Scientists at SNRE, together with those from the University of California, Berkeley, Colorado State University, Northern Arizona University and Oregon State University collaborated on the data analysis that led to these findings.

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