Oct. 14, 1998 Scientists Investigate Smoke As Trigger For Seed Germination
To the dismay of many Californians, and most recently Floridians, nearly every summer it happens. Trees alight in a fiery blaze, resulting in millions of dollars in property damage, displaced families, and in some instances the loss of life. All that's left after the last ember dies out is a charred, skeleton forest. Yet the next generation of forest lies beneath the scorched soil as once dormant seeds are awakened. In the October issue of Ecology, scientists investigate the mechanisms behind fire-triggered seed germination, and focus specifically on the role of smoke.
Scientists have previously reported that heat shock and charred wood induce germination in dormant seeds. In their study of California chaparral, Jon E. Keeley, of the USGS Biological Resources Division, and C. J. Fotheringham, of California State University, show that smoke also triggers germination in deeply dormant seeds.
Keeley and Fotheringham compared seed characteristics of species stimulated by smoke to those stimulated by heat shock, and the different mechanisms behind germination. Seeds that germinate after exposure to smoke are distinctly different from those that do not:
* outer seed coats are highly textured * have a poorly developed outer cuticle * are missing dense tissue in the coat of the seed * have a membrane which allows water to pass through but not larger particles
Smoke triggers germination directly by penetrating the seed, as well as indirectly, by vapor or liquid transfer from soil to seeds. The scientists found, within the smoke-stimulated plants, that a variety of factors trigger germination. Such factors are: charred wood, Nitrogen dioxide, duration of exposure to smoke, soil content and moisture level, and the influence of day and night. In some species, exposure to smoke alone was enough to cause a seed to germinate. In others, a combination of factors was necessary for germination to take place. Keeley and Fotheringham conclude that the different responses triggered among plants may suggest fire behavior has an important ecological impact on postfire communities by influencing which plants will prosper and reclaim the land.
October's issue of Ecology also highlights the effects of large mammals on soil nutrient movements.
In one such article, M. Ben-David and colleagues of the University of Alaska and Oregon State University explore the effects of scent-marking behavior of river otters on surrounding terrestrial plants in south-central Alaska. River otters deposit urine and feces at specific sites along the coast, known as latrines. The researchers found that plants at latrine sites had larger concentrations of Nitrogen than those off site. They also discovered that the concentration of Nitrogen in plants located in latrines matched the concentration of fish in the otters' diet. By enriching the soil with Nitrogen (fertilization), the researchers believe that river otters may influence the plant community composition.
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