Mechanism of smoke‐induced seed germination in a post‐fire chaparral annual

Abstract

1 Smoke‐stimulated germination in the post‐fire flora of California chaparral does not appear to be triggered by nitrate. Application of freshly prepared unbuffered KNO 3 solutions (pH c. 6.2) failed to enhance germination of five populations of Emmenanthe penduliflora or one Phacelia grandiflora population, regardless of light or stratification conditions. 2 KNO 3 buffered at acidic pH (or unbuffered solutions equilibrated with atmospheric CO 2 ) did induce germination, but KNO 3 solutions at pH 7 failed to induce germination. Induction of germination is therefore not due to the nitrate ion per se , but rather to high [H + ], although 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 germination response to KNO 3 was affected by the type of filter paper used and this may be linked to differences in pH. 4 NO 2 , at concentrations present in biomass smoke, was highly effective at inducing germination, and other oxidizing agents also induced germination. 5 Several growth regulators, including nitrite and gibberellin, were stimulatory only at acidic pH, but KCN was stimulatory across a broad pH range. 6 Germination decreased at smoke exposures longer than a few minutes. Also, smoked water samples effective at breaking dormancy were acidic and were less effective when buffered to pH >7. 7 Physical scarification of the seed coat induced germination but the effect was not due to penetration of a water barrier, or to enhanced oxygen uptake or to wound responses such as CO 2 or ethylene production. 8 Different effects of the gibberellin inhibitor CCC (chlorocholine chloride) suggested that the mechanisms of scarification‐induced and smoke‐induced germination may differ. 9 We conclude that either oxidizing gases in smoke and/or acids generated on burnt sites play a role in germination of post‐fire annuals in chaparral.