Smoke Exposure Induces Seed Germination
Posted February 1, 1998
The dry chaparral blazes with fire after a lightning strike. The dense vegetation burns to create a hot fire, heating and charring the seeds of certain plants. Some
seeds actually require this kind of heat to destroy the outer covering of the seed. When a fire passes through the chaparral, it heats seeds like these; at the same time, it burns off
the taller, older plants that would shade out newly germinated seedlings. Because the fire has cleared the land, the seeds have adequate sunlight. At the first rainfall, these seeds
germinate.
Recent studies show that some of the seeds that germinate after a hot fire are responding to chemicals in smoke, rather than to heat. Nitrogen dioxide and other chemicals
in smoke were shown to influence the germination of whispering bells, a plant species that grows quickly after fires in the California chaparral. In an experiment, the seeds of this
plant were exposed to smoke in a variety of ways. Some seeds were treated with smoke alone; others were treated with smoke-treated filter paper; still others were treated with smoke-treated
sand, water, and water vapor. No matter how the smoke was delivered to the seeds, between 80 and 100 percent of the seeds germinated when exposed to smoke for just 30 seconds —
without any fire at all.
These findings have been confirmed with tests of plant seeds from other parts of the world that have chaparral-like vegetation and hot, dry summers. In southern
California, the Great Basin in Utah, South African savanna, and in the Australian heath, plants have been found that germinate when exposed to smoky wood. The discovery that some seeds
germinate in response to the nitrogen dioxide in smoke has led researchers to some concern about plants found in areas with air pollution. Nitrogen dioxide is a major component of air
pollution from automobiles. Scientists worry that air pollution in places such as Los Angeles contains enough nitrogen dioxide to begin germination of some seeds. Without fire to burn
off the vegetation and enable sunlight to reach the seeds, germinated seeds may not survive. Then, when fire does occur, there may not be any viable seeds left to repopulate the environment.
References
Keeley, Jon E. and C.J. Fotheringham. "Trace Gas Emissions and Smoke-Induced Seed Germination." Science, May 23, 1997, Vol. 276, pp. 1248-1250.
Mlot, C. "Where There's Smoke, There's Germination." Science News, May 31, 1997, Vol. 151, p. 334.
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