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January 2, 2002
Competition for Resources Influences Species Diversity in Plant Communities

WOODS HOLE, MA—How plants compete for a limiting soil resource—such as nitrogen— influences the diversity and dominance of plant species within a community, reports a paper that will be published in the January 3, 2002, issue of the journal Nature.

Scientists, including four from the Marine Biological Laboratory's Ecosystems Center, studied tundra plants at Toolik Lake, Alaska, whose growth is limited primarily by the availability of soil nitrogen. The researchers found that the plants in this community took up nitrogen at different times, depths, and in different forms. They also found that the most productive plant species used the most
abundant forms of nitrogen while less productive species used less abundant forms.

Ecologists have long been intrigued by the ways species living in the same community divide limiting resources and thereby promote diversity by reducing competition. This resource partitioning, or "niche differentiation," is an important determinant of species diversity and composition in animal communities. However, its importance in structuring plant communities has been difficult to determine, mostly because of difficulties in measuring how plants compete for below-ground resources. The researchers overcame this problem by injecting plots of tundra with 15N, a rare stable isotope of nitrogen. By injecting different chemical forms of 15N at different times and soil depths, they were able to trace how plants took up naturally occurring forms of soil nitrogen. The tracer study provides a clearer view of below-ground competitive interactions than existed previously, and establishes a better way to address fundamental questions about plant species diversity. "Although other studies have shown spatial, temporal or chemical differences in resource use among plant species living within the same community, this study is the first to demonstrate the mechanisms by which such differences influence species diversity and composition," said lead
author Robert McKane, an ecologist with the Environmental Protection Agency in Corvallis, Oregon. The work began while McKane was a research associate at the Marine Biological Laboratory's Ecosystems Center.

The Marine Biological Laboratory (MBL) is an independent scientific institution, founded in 1888, that undertakes thehighest level of creative research and education in biology, including the biomedical and environmental sciences. The research of the MBL's Ecosystems Center, which was established at the MBL in 1975, is focused on the study of natural ecosystems. Among the key environmental issues being addressed are: the ecological consequences of global climate change; tropical deforestation and its effects on greenhouse gas fluxes; nitrogen saturation of mid-latitude forests; effects of acid rain on North American lakes; and pollution and habitat destruction in coastal ecosystems of the United States.