No abstract

In Mediterranean fire-prone ecosystems, annual species specific to post-fire habitats should have a soil seed bank and should be able to germinate after a fire. Therefore, various fire-related cues can be expected to stimulate germination in post-fire annuals. Germination patterns of the rare annual Chaenorhinum rubrifolium (Plantaginaceae) were examined in response to mechanical scarification, heat shock, aqueous smoke, nitrogenous compounds, gibberellic acid, karrikinolide (KAR1), and mandelonitrile (a cyanohydrin analogue, MAN) under dark and photoperiod conditions in the laboratory. Combinations of these treatments were also included in the experiment. Strong physiological dormancy in the seeds of C. rubrifolium was partially broken by several fire-related germination cues, including smoke and nitrate, under light conditions. KAR1 and MAN also stimulated germination, and the highest improvement in germination was achieved in the KAR1 treatment in the presence of light. Heat shock + smoke and KAR1 + MAN combinations had positive synergetic and additive effects on germination under light conditions, respectively. The light played a crucial role in the promotion of germination. The results suggest that multiple fire-related cues operate to stimulate germination in C. rubrifolium, an annual species from the Mediterranean Basin. However, the species may have a broader germination niche than a fire-restricted one.

The role of smoke in fire-stimulated germination in the Mediterranean Basin has often been underestimated. A few records on smoke-enhanced germination are present in Mediterranean Lamiaceae species, but there is still a shortage of information to allow generalizations about this family to be made. To test the hypothesis that smoke enhances germination in Mediterranean Lamiaceae species, we performed a germination experiment, including aqueous smoke treatments in various concentrations (1:1, 1:10 and 1:100) on seven eastern Mediterranean Lamiaceae taxa. Six of the studied taxa (Lavandula stoechas, Origanum onites, Phlomis bourgaei, Stachys cretica ssp. smyrnaea, Satureja thymbra, Teucrium lamiifolium ssp. stachyophyllum) showed significant increments in germination percentage in at least one smoke treatment, as compared to the control. Moreover, L. stoechas, S. thymbra and T. lamiifolium ssp. stachyophyllum displayed faster germination in at least one smoke treatment than in the control. Of the species showing significant increments in germination percentages after aqueous smoke application, at least one single concentration of smoke solution did not stimulate germination, except in L. stoechas and S. thymbra which responded positively to all smoke treatments. Therefore, the concentration of aqueous smoke that improved germination was speciesspecific. Our results contribute to the current limited knowledge on smoke-enhanced germination in Mediterranean Lamiaceae, and support the idea that smoke is an important germination cue for this family.

The promoting effect of smoke-derived chemicals (e.g. karrikinolide and cyanohydrin) on germination in many plants from Mediterranean-type ecosystems such as South Africa and southwestern Australia is well documented. However, very little is known about (1) the relative importance of different compounds and their possible interactive effects, (2) their role in enhancing seedling growth in wild plants, and (3) their effect on the germination of plants in the Mediterranean Basin. To fill these gaps in knowledge, we performed experiments to evaluate the effect of smoke water, karrikinolide, mandelonitrile (a cyanohydrin analogue), potassium nitrate and gibberellic acid on the germination and seedling growth of 37 species from the Mediterranean Basin. The results suggest that germination and/or seedling growth of 21 species are enhanced by at least one of the fire-derived chemicals. There were positive correlations between most of the compounds tested in terms of germination response, but synergetic and inhibitory effects were also detected. Stimulation of germination was most prominent in species with annual life cycles. Fire-derived chemicals were more effective in stimulating root growth than shoot growth. In conclusion, we provide novel evidence that the recruitment of different Mediterranean species may be enhanced by different smoke compounds, and that synergetic and inhibitory effects of chemical compounds are important in the germination ecology of plants.