Smoke affects the germination of native grasses of New South Wales

The germination responses to plant-derived smoke of seeds of 20 native gras s species from New South Wales, Australia, were tested under laboratory con ditions. The species belonged to 14 genera including Bothriochloa, Chloris, Cymbopogon, Danthonia, Dichanthium, Digitaria, Eragrostis, Eriochloa, Micr olaena, Panicum, Paspalidium, Poa, Stipa and Themeda. The interaction betwe en smoke and husk-imposed dormancy was examined by removing the floral stru ctures surrounding the seeds, when sufficient seeds were available. Smoke w as shown to be an important environmental stimulus for breaking the dormanc y of native grasses; however, the response differed considerably between di fferent genera and between species of the same genus. For almost half of th e species, smoke significantly increased the germination percentage. Panicu m decompositum showed the greatest response, with germination increasing fr om 7.7 to 63.1% when smoke was applied. Panicum effusum had no germination in the absence of smoke, but 16.7% germination when smoke was applied. Stip a scabra subsp. scabra had germination significantly reduced by smoke from 30.2 to 19.9%. Five species had their germination rate, but not the final g ermination percentage, affected by smoke, and a third of the species were u naffected by smoke. For five of the species, Chloris ventricosa, Dichanthiu m sericeum, Panicum decompositum, Poa labillardieri and Stipa scabra subsp. falcata, this is the first report of a smoke-stimulated germination respon se. For those species with germination promoted by smoke, retention of the covering structures did not prevent smoke stimulation of germination. Sowin g smoke-treated husked seeds is likely to be preferable as it would still p romote greater germination, whereas dehusking seeds can result in the seeds being more susceptible to desiccation and fungal attack in the field. It i s suggested that other grassland communities that respond to pyric conditio ns may also contain species that respond to smoke.