MECHANISM OF SMOKE-INDUCED SEED-GERMINATION IN A POSTFIRE CHAPARRAL ANNUAL

1 Smoke-stimulated germination in the post-fire flora of California ch aparral does not appear to be triggered by nitrate. Application of fre shly prepared unbuffered KNO3 solutions (pH c. 6.2) failed to enhance germination of five populations of Emmenanthe penduliflora or one Phac elia grandiflora population, regardless of light or stratification con ditions. 2 KNO3 buffered at acidic pH (or unbuffered solutions equilib rated with atmospheric CO2) did induce germination, but KNO3 solutions at pH 7 failed to induce germination. Induction of germination is the refore not due to the nitrate ion pet se, but rather to high [H+], alt hough buffered controls gave weak germination at low pH, suggesting a role for H+ plus nitrate. However, other anions such as sulphate were equally as effective as nitrate at breaking dormancy. 3 The germinatio n response to KNO3 was affected by the type bf filter paper used and t his may be linked to differences in pH. 4 NO2, at concentrations prese nt in biomass smoke, was highly effective at inducing germination, and other oxidizing agents also induced germination. 5 Several growth reg ulators, including nitrite and gibberellin, were stimulatory only at a cidic pH, but KCN was stimulatory across a broad pH range. 6 Germinati on decreased at smoke exposures longer than a few minutes. Also, smoke d water samples effective at breaking dormancy were acidic and were le ss effective when buffered to pH >7. 7 Physical scarification of the s eed coat induced germination but the effect was not due to penetration of a water barrier, or to enhanced oxygen uptake or to wound response s such as CO2 or ethylene production. 8 Different effects of the gibbe rellin inhibitor CCC (chlorocholine chloride) suggested that the mecha nisms of scarification-induced and smoke-induced germination may diffe r. 9 We conclude that either oxidizing gases in smoke and/or acids gen erated on burnt sites play a role in germination of post-fire annuals in chaparral.