Fire effects on seed germination: Heat shock and smoke on permeable vs impermeable seed coats

Abstract

Flammable ecosystems host plants with different strategies in response to fire, such as increasing germination after the exposure to smoke and dormancy breaking by heat shocks. Cerrado is a fire-prone ecosystem, but less is known about fire-related germination cues compared to Mediterranean-like ecosystems. Here, we hypothesize that seeds with a permeable tegument (Melastomataceae) respond positively to smoke (increase in germination), while species with physical dormancy (Fabaceae) have dormancy broken by exposure to high temperatures. We exposed seeds from Fabaceae and Melastomataceae species to high temperatures and smoke solution to simulate fire. Finally, we combined the two treatments (heat shock + smoke). Our results showed that seeds of two legumes (Harpalyce sp. and Mimosa leiocephala) had their physical dormancy broken when exposed to high temperatures, while one Fabaceae (Mimosa somnians) and two Melastomataceae showed an increase in germination when exposed to smoke solution. Lastly, four Fabaceae and two Melastomataceae species responded when combining heat shock and smoke. Contrary to our predictions, the responses to fire stimuli in Cerrado species did not show a clear response pattern, as those found in Mediterranean vegetation, probably due to differences in fire regime. However, we showed novel results about smoke stimulation for some species and positive effects of combined treatments. Thus, Cerrado seeds differ in response to fire, showing that cues for germination are more complex than previously thought, differing from other fire-prone ecosystems.