Smoke-induced seed germination in Texas grassland species

Background/Question/Methods

Seed dormancy is a common trait among plant species that inhabit environments characterized by periodic disturbance. Dormancy and the cues required for germination allow plants to avoid unfavorable environmental conditions. In fire-prone ecosystems, many species require signals such as heat or smoke to cue seedling establishment to the relatively favorable post fire environment. Smoke-induced seed germination has been of particular interest and is relatively common in South Africa, California and Australia. 

Grassland ecosystems are often maintained by recurring fire and many grassland species are considered well adapted to fire. Despite this, smoke-induced germination has been studied much less in grasslands than in shrublands subject to crown fire. Central Texas grasslands are maintained by fire and, although grasses are not generally known for seed dormancy, many grassland forbs are related to species in which smoke-stimulated germination has been reported. We tested 17 species native to the Edwards Plateau of Texas for seed dormancy and smoked-stimulated germination using smoke treatments of 4 and 8 minutes and untreated controls. All treatments were subject to cold vernalization for 4 weeks after smoke exposure. We selected species from genera in which smoke stimulated germination had been previously reported: Coreopsis, Echinacea, Liatris (Asteraceae), Phacelia (Hydrophyllaceae), Salvia (Lamiaceae), Callirhoe (Malvaceae), Phlox (Polemoniaceae), and Bouteluoa (Poaceae). 

Results/Conclusions

In our species, most showed no dormancy, and of those that exhibited dormancy, only two species exhibited smoke-stimulated germination. Both Salvia species tested (S. farinacea and S. coccinea) showed germination increases of approximately 8-fold when exposed to 4 minutes of smoke. Both are common species in the Edwards Plateau and this is the first report of smoke-stimulated germination. Although there is one report of smoke-induced germination in populations of B. curtipendula from tallgrass prairie, we found no dormancy in any Bouteluoa species. These results suggest that smoke may be an important germination cue for two common Texas Salvia species, but otherwise does not appear to be a widespread cue for Texas grassland species. We are currently testing for heat cues among those species which exhibit dormancy and exploring the phylogenetic pattern of fire-related germination cues.