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

Abstract

Dormancy and germination requirements determine the timing and magnitude of seedling emergence, with important consequences for seedling survival and growth. Physiological dormancy is the most widespread form of dormancy in flowering plants, yet the seed ecology of species with this dormancy type is poorly understood in fire-prone vegetation. The role of seasonal temperatures as germination cues in these habitats is often overlooked due to a focus on direct fire cues such as heat shock and smoke, and little is known about the combined effects of multiple fire-related cues and environmental cues as these are seldom assessed in combination. We aimed to improve understanding of the germination requirements of species with physiological dormancy in fire-prone floras by investigating germination responses across members of the Rutaceae from south eastern Australia. We used a fully factorial experimental design to quantify the individual and combined effects of heat shock, smoke and seasonal ambient temperatures on germination of freshly dispersed seeds of seven species of Boronia, a large and difficult-to-germinate genus. Germination syndromes were highly variable but correlated with broad patterns in seed morphology and phylogenetic relationships between species. Seasonal temperatures influenced the rate and/or magnitude of germination responses in six species, and interacted with fire cues in complex ways. The combined effects of heat shock and smoke ranged from neutral to additive, synergistic, unitive or negative and varied with species, seasonal temperatures and duration of incubation. These responses could not be reliably predicted from the effect of the application of single cues. Based on these findings, fire season and fire intensity are predicted to affect both the magnitude and timing of seedling emergence in wild populations of species with physiological dormancy, with important implications for current fire management practices and for population persistence under climate change.

Maximizing rice husk waste for Daucus carota production

“…The applied treatments influenced carrot seedling emergence as indicated by the observed significant effects. Time to seedling emergence is the result of a complex interaction of ambient weather conditions, soil, seed and seedling characteristics (Mackenzie et al 2016). This interaction can be influenced by the production environment which might improve or reduce seedling emergence.…”

Broad‐scale patterns in smoke‐responsive germination from the south‐eastern Australian flora

“…At the same time, there have been comparatively few studies of smoke‐promoted germination in the south‐eastern Australian flora. South‐eastern Australia does not fit the Mediterranean‐type climate classification; it has a temperate climate with rainfall and hence seed germination is possible throughout the year (Mackenzie, Auld, Keith, Hui, & Ooi, ). South‐eastern Australia is considered fire‐prone (Thomas, Morris, & Auld, ).…”

Evidence for direct effects of fire‐cues on germination of some perennial forbs common in grassy ecosystems

“…; Mackenzie et al . ; Collette & Ooi ). These findings suggest that germination of D. revoluta may be dependent on exposure to warm moist conditions in the soil seed bank prior to fire.…”

“…; Mackenzie et al . ), although there has been little investigation in other fire‐prone environments.…”