Smoke-induced seed germination in California chaparral

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

Nitrate and ammonium ion (KN[O.sub.3] and N[H.sub.4]N[O.sub.3], each at 1, 10, and 100 mol/[m.sup.3]) and gibberellic acid (1, 5, and 10 mmol/[m.sup.3]) solutions were prepared from freshly purified water or in buffered solutions of 25 mol/[m.sup.3] citrate-phosphate (pH range: 2.5-5), MES (2-[N-Morpholino]ethanesulfonic acid) buffer (pH 6; Sigma M-5287 [Sigma Chemical Company, Saint Louis, Missouri, USA]), or HEPES (N-[2-Hydroxyethyl] piperizine-N[prime]-[ethanesulfonic acid]) buffer (pH 7 and 8; Sigma H-7523) and 2.0 mL added to a petri dish with filter paper. Hydrogen peroxide, nitric acid, sulfuric acid, and acetic acid were tested by soaking seeds in different molarity solutions for 6, 12, 18, or 24 h, followed by two distilled water rinses and then sowing on filter paper in petri dishes.

A potential confounding effect in these experiments involving aqueous solutions was the hydrophobicity of some species, which resulted in seeds floating on the solution surface. This effect was readily overcome by soaking seeds in lipase solution. Lipase concentrations of from 400-4000 U/mL (Sigma L-8525) (where U = moles of substrate converted per minute per milligram protein) in 50 mol/[m.sup.3] HEPES pH 7.7 buffer were effective in rapidly overcoming the hydrophobic character of the seed coat. All chemical treatments and water-uptake experiments were tested both with and without prior lipase treatment.

TABLE 1. Chaparral species demonstrating statistically significant
smoke-induced germination (nomenclature according to Hickman
[1993]). Seeds of all annual species were collected in southern
California from first-year burns, and others were collected on 2-3
yr old burns. Seeds were 6-18 mo old at the time of experiments.

Family                     Species              Growth form

Asteraceae         Chaenactis artemisiifolia    Annual
Boraginaceae       Cryptantha clevelandi        Annual
                   C. micrantha                 Annual
Brassicaceae       Caulanthus heterophyllus     Annual
Caryophyllaceae    Silene multinervia           Annual
Hydrophyllaceae    Emmenanthe penduliflora      Annual
                   Eucrypta chrysanthemifolia   Annual
                   Phacelia grandiflora         Annual
                   P. minor                     Annual
Lamiaceae          Salvia apiana                Shrub
                   S. columbariae               Annual
                   S. leucophylla               Shrub
                   S. mellifera                 Shrub
Loasaceae          Mentzelia micrantha          Annual
Onagraceae         Camissonia californica       Annual
Papaveraceae       Romneya coulteri             Suffrutescent(*)
Polemoniaceae      Allophyllum glutinosum       Annual
Scrophulariaceae   Antirrhinum coulterianum     Annual
                   A. kelloggii                 Annual
                   A. nuttallianum              Annual
                   Mimulus clevelandii          Suffrutescent(*)
                   Penstemon centranthifolius   Suffrutescent(*)

* Suffrutescent = herbaceous with woody caudex.