Heat increases germination of water-permeable seeds of obligate-seeding Darwinia species (Myrtaceae)

Abstract

We examined the response of seeds to heat in four geographically restricted and one widespread species of shrubby Darwinia from the fireprone region of southeastern Australia. These shrubs are killed by fire and rely on seed germination after a fire to maintain populations. We replicated the germination trials across several sites and several fruiting seasons for most species. Seeds had a high level of viability and were largely dispersed in a dormant state, except in D. glaucophylla, where seed dormancy varied significantly across fruiting seasons. The indehiscent fruit of all species readily imbibes moisture when wet and seeds are not considered to be 'hard-seeded'. All species had increased seed germination in response to a limited range of heating temperatures (generally 80-100°C). Higher temperatures killed increasing proportions of seeds. This pattern was broadly consistent across species, population and seasons, although the proportion of seeds whose germination was promoted by heat varied from high (D. diminuta, D. fascicularis, D. glaucophylla) to moderate (D. biflora, D. procera). Our work highlights the importance of heat as a mechanism for influencing germination in species that are not hardseeded. Consequently, soil temperatures during a fire should strongly influence post-fire germination levels in Darwinia. The roles of other cues that promote germination, i.e. smoke, seasonal temperatures and their interactions with heat, remain to be investigated.

Litter addition decreases plant diversity by suppressing seeding in a semiarid grassland, Northern China

“…Moreover, litter removal can indirectly inhibit seedling recruitment by reducing soil moisture (Figure b). Moreover, the increase in soil temperature inhibits seedling recruitment by sharply decreasing seed vigor (Auld & Ooi, ; Avhad & Marchetti, ; Lombraña, Porceddu, Dettori, & Bacchetta, ), or accelerating seedlings death at early stage (Binder & Fielder, ; Harper & O'Reilly, ). Litter removal does not regulate seedling recruitment by affecting ST because ST did not increase in litter removal treatment.…”

The Effect of Seasonal Ambient Temperatures on Fire-Stimulated Germination of Species with Physiological Dormancy: A Case Study Using Boronia (Rutaceae)

“…The promotive effect of heat shock on the germination of hard-seeded (physically dormant) species is widely known, however, there are relatively few reports of positive responses to heat shock in species with PD e.g. some Apiaceae [ 14 ], Ericaceae [ 29 , 37 ], Haemodoraceae [ 24 , 45 ], Lamiaceae [ 29 ], Myrtaceae [ 68 ], Poaceae [ 41 ], Proteaceae [ 39 ] and Rutaceae [ 57 , 69 , 87 ]. In the present study, we found that heat shock was essential for germination of B .…”

“…Heat shock treatments were applied by placing seeds in aluminium foil cups and exposing them to 90°C in a pre-heated oven for 10 minutes. This temperature and duration of heating falls within the range of conditions experienced by seeds in the upper layers of the soil during the passage of fire [ 67 ], and has been reported to promote germination of a wide range of local species [ 27 , 68 ], including several Rutaceae [ 69 ]. Smoke treatments were applied by placing seeds in aluminium foil cups inside a 60 L plastic chamber and piping in aerosol smoke for 10 minutes.…”

Seed Germination in Cistus ladanifer: Heat Shock, Physical Dormancy, Soil Temperatures and Significance to Natural Regeneration

“…This range of optimal temperatures for final germination is not exclusive of C. ladanifer and is found in a variety of other species from fire-prone ecosystems [26,45,46,47,48,49,50] strongly suggesting that it represents what may be a generalized adaptive response to recurrent fires. However the discussion of whether it is in fact an adaptation or an exaptation [51,52,53,54] is beyond the scope of this paper.…”

“…Fire effects on soil are known to be extremely variable and heterogeneous either at soil surface or at deeper levels [36] and it has been suggested that lethal temperatures occur in soils during fires but generally confined to the soil surface [45,74]. To our knowledge no data exist on time-temperature distributions in soil during fires in C. ladanifer stands.…”