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The Seedy Side of CO2
5 April 2001 7:00 pm
Some trees may reproduce earlier and more abundantly in a world pumped up with carbon dioxide, according to a new study. The research adds to growing evidence that at least some plants can profit from hikes in CO2 levels--but these changes may decrease forest biodiversity.
released from vertical towers in a large open-air experiment at Duke.
CREDIT: CO2 ENRICHMENT RESEARCH
Atmospheric CO2 has increased by nearly 40% in the last century and almost certainly will continue to rise. For more than 2 decades, biologists have been working to understand how plants respond. Crops clearly respond with faster growth and higher yields. But research on wild plants, conducted in growth chambers, greenhouses, and small outdoor open-top chambers, have yielded more variable results and have been hampered by the artificial conditions of the experiments.
To overcome this obstacle, Duke University biologists Shannon LaDeau and James Clark used an experimental forest equipped to simulate changes in CO2. The gas is released from large vertical pipes that tower over six 150-square-meter plots of mature loblolly pine (Pinus taeda). Half of the stands are grown at ambient CO2 levels and the other half at the 560-ppm concentration expected by 2050. Otherwise, conditions in the experimental and control stands are identical, and all trees are exposed to whatever weather Mother Nature dishes out. Earlier results from the same forest had indicated that high CO2 levels can spur faster photosynthesis and growth in loblolly pines. LaDeau and Clark wondered what the effect of high CO2 levels would be on reproduction.
They found that loblolly pines grown for 3 years at high CO2 levels are twice as likely to be reproductively mature, and produce three times as many cones and seeds, as trees in today's environment. In addition, trees in the high-CO2 plots produced more seeds than did trees of the same size in control plots, suggesting that they were putting a higher percentage of their carbon currency into reproduction.
The report, which appears in the 6 April issue of Science, is an "elegant demonstration that CO2's stimulatory effect on photosynthesis and growth carries over to reproduction," says Peter Curtis, a biologist at Ohio State University in Columbus. These effects could lead to wholesale changes in forest ecosystems, he adds. "My suspicion is that forest communities will become less diverse as aggressive, fast-growing trees become more abundant"--shifts that would have cascading effects throughout the ecosystem.