The Induction of Germination by Smoke

Fire is an important component of several ecosystems. For many plant species, fire and its associated effects are required for seed germination. Stimulating factors include heat, charred wood, and smoke. The chemicals in smoke may cause seed germination through different mechanisms. For the most part, though, the chemical structures and mechanisms involved in smoke induced germination remain poorly understood.

In a number of natural systems, fire acts as a "dominant ecological and evolutionary influence (7:1608-1621)." Brandegee (1891) first noted the spectacular wildflower displays that occur during the initial growing season following a chaparral wildfire. Indeed, over 200 species of annuals, herbaceous perennials, and short-lived suffrutescents have been observed growing in areas previously burned. This temporary vegetation derives primarily from seed or vegetative parts which are already present in the soil. The seeds of many plant species remain in a state of dormancy until stimulated by fire. These fire-following plants may exhibit varying degrees of dormancy. Moreover, the germination of their seeds may be induced by different types of fire-related stimuli (5:240-249). These processes synchronize the plants' regrowth, reproduction, and germination with the immediate post-fire environment. Such synchronization may provide the plants with the following benefits: (1) a potentially elevated nutrient supply (in partic

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are known to be capable of breaking seed dormancy. These include both simple compounds such as potassium nitrate, and more complicated molecules such as the plant hormone, gibberellin (9:90-99). The active ingredient in charred wood has been found to be water soluble and capable of passing through a 0.2 micrometer nitrocellulose filter. In addition, the fact that neither completely ashed wood nor Hoagland's solution has the same stimulatory effect suggests that the agent is an organic compound. Researchers have also observed that heating the wood of many ligneous species for 30 minutes at 175(C produces a stimulatory effect. Moreover, heating hemicellulose xylan to 175(C for 10 minutes also stimulates germination. This implies that the active ingredient derived from charred wood is either an oligosaccharide or some other carbohydrate. Finally, recent investigations have observed that the stimulating compound in charred wood is extractable in the following solvents: (1) methane; (2) acetone; and (3) hexane. Activity in both polar and nonpolar solvents indicates that this type of germination induction may involve more than one compound (6:81-115). In addition to heat and charred wood, exposure to smoke is also known to st
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Approximate Word count = 1791
Approximate Pages = 7 (250 words per page)