Diversity boosts plant growth.

• Author: Runyan, Curtis
• Position: Environmental Intelligence

A new study, published in the 12 April 2001 issue of the journal Nature, finds that undermining biodiversity may make coping with climate change more difficult. Over the course of two years, the researchers, led by University of Minnesota ecologists Peter Reich and David Tilman, subjected plots of different plant diversities to increased levels of nitrogen and carbon dioxide ([CO.sub.2]). The plots with 16 plants consistently outgrew plots with a diversity of 9, 4, or only 1 species (see graph).

Largely the results of the burning of fossil fuels and the application of fertilizers to crops, carbon and nitrogen levels are increasing at a rapid rate. The level of atmospheric [CO.sub.2], the most important greenhouse gas, has risen by 31 percent since 1750. And the level of biologically active nitrogen--elemental nitrogen (N) that can be absorbed by plants because it has been "fixed" as ammonium ([NH.sub.4]) or nitrate ([NO.sub.3])--is thought to have doubled since the 1950s

Through the 1998 and 1999 growing seasons, the researchers monitored 296 plots at the Cedar Creek Natural History area in Minnesota, each planted with one of the four different seed mixes. Using giant plastic tubing that vented regulated amounts of carbon dioxide into the air, half of the plots were provided with levels of the gas expected to be prevalent by the end of the century--560 parts per million (the current level is 369 ppm). Half of the plots were also fertilized with increased the levels of nitrogen expected in the future.

While all of the plots that were fed increased levels of carbon dioxide and nitrogen experienced a boost in growth, the...