Smoke-induced seed germination in California chaparral

Ecology, Oct, 1998 by Jon E. Keeley, C.J. Foteringham

Gaseous transfer of smoke chemicals is apparent from the high germination induced in both Emmenanthe and Romneya seeds when untreated moist seeds were exposed indirectly to vapors emitted from moistened smoked sand (or filter paper) [ILLUSTRATION FOR FIGURE 4C OMITTED]. Complete germination was also observed when dry seeds were exposed to gases emitted from dry media that had previously been exposed to smoke (data not shown). based on this observation, we hypothesized that charred wood induced germination by emitting vapors that also occur in smoke. Exposure of Emmenanthe, Romneya, and Caulanthus seeds to charred-wood vapors induced 79%, 44%, and 38% germination, respectively (P [less than] 0.001 over controls).

Soil storage effects

Seeds of four species that completely failed to germinate in the initial smoke experiments were buried outdoors for 1 yr, dried, and then smoke-treated. Following this long-term soil storage, three of these species - Dendromecon, Dicentra, and Trichostema - were stimulated to germinate by smoke treatment [ILLUSTRATION FOR FIGURE 6 OMITTED], but soil-stored seeds of the fourth species, Phacelia brachyloba, still failed to germinate (not shown). Several other species exhibiting smoke-stimulated germination in the original experiments (from room-stored seed) were also buried for 1 yr and then re-tested. In some species, e.g., Emmenanthe, there was no change in germination response. Buried Romneya seeds were found to be smoke-stimulated at shorter durations of smoke exposure, and others, e.g., Phacelia minor, exhibited significantly (P [less than] 0.001) higher smoke-induced germination following long-term soil burial (data not shown).

Seed coat scarification

The effect of physical scarification of the seed coat exhibited three patterns in smoke-induced species. (1) In the majority of species tested, scarification was sufficient to induce high germination (Table 3). (2) In Romneya, scarification alone was largely ineffective, but, scarification plus gibberellic acid (GA) induced complete germination - though scarification plus potassium nitrate, ethylene, or carbon dioxide failed to stimulate germination. (3) In Dicentra, Dendromecon, and Phacelia brachyloba neither scarification, nor scarification GA, induced germination in either room-stored or soil-stored seed.

Exposure to acids, which may have caused chemical scarification of the seed coat, also induced germination in some smoke-stimulated species, but not others [ILLUSTRATION FOR FIGURE 7 OMITTED]. Emmenanthe germinated well with pulses of 10 mol/[m.sup.3] of acid, and Silene multinervia germinated best with 100 mol/[m.sup.3] of acid [ILLUSTRATION FOR FIGURE 7 OMITTED]. On the other hand, Romneya failed to respond to any acid treatment [ILLUSTRATION FOR FIGURE 7 OMITTED], including continuous application of 50 or 100 mmol/[m.sup.3] of acids (not shown). Although not illustrated, similar results were obtained with acetic acid (Emmenanthe = 77% germination with 10 mol/[m.sup.3], Romneya = 0% with 1, 10, and 100 mol/[m.sup.3] and Silene = 66% with 100 mol/[m.sup.3]). Other species induced to germinate by acid treatment were Phacelia grandiflora (23% with a 6-h pulse of 10 mol/[m.sup.3] of nitric acid) and Caulanthus (100% with an 18-h pulse of 100 mol/[m.sup.3] of nitric acid). In these latter two species sulfuric acid was about half as effective, and acetic acid was ineffective.