A field perspective on effects of fire and temperature fluctuation on Cerrado legume seeds

Abstract

Information from a field perspective on temperature thresholds related to physical dormancy (PY) alleviation and seed resistance to high temperatures of fire is crucial to disentangle fire- and non-fire-related germination cues. We investigated seed germination and survival of four leguminous species from a frequently burned open Neotropical savanna in Central Brazil. Three field experiments were conducted according to seed location in/on the soil: (1) fire effects on exposed seeds; (2) fire effects on buried seeds; and (3) effects of temperature fluctuations on exposed seeds in gaps and shaded microsites in vegetation. After field treatments, seeds were tested for germination in the laboratory, together with the control (non-treated seeds). Fire effects on exposed seeds decreased viability in all species. However, germination of buried Mimosa leiocephala seeds was enhanced by fire in an increased fuel load treatment, in which we doubled the amount of above-ground biomass. Germination of two species (M. leiocephala and Harpalyce brasiliana) was enhanced with temperature fluctuation in gaps, but this condition also decreased seed viability. Our main conclusions are: (1) most seeds died when exposed directly to fire; (2) PY could be alleviated during hotter fires when seeds were buried in the soil; and (3) daily temperature fluctuations in gaps also broke PY of seeds on the soil surface, so many seeds could be recruited or die before being incorporated into the soil seed banks. Thus seed dormancy-break and germination of legumes from Cerrado open savannas seem to be driven by both fire and temperature fluctuations.

Resilience and restoration of tropical and subtropical grasslands, savannas, and grassy woodlands

“…A particular gap in restoration research, little is known about the role of fire in the reproduction and establishment of savanna grassland plants. Initial studies on heat shock simulated in the laboratory suggest that fire does not break seed dormancy, stimulate germination, or kill the seeds (Le Stradic et al ., ; Fichino et al ., ; Zupo, Baeza & Fidelis, ), whereas in field experiments, although many seeds died, fire indirectly promoted germination of surviving seeds, by reducing vegetation cover, which increased soil surface temperature fluctuation (Daibes et al ., ). In a laboratory study of grasses of southern Africa, Ghebrehiwot et al .…”

“…A particular gap in restoration research, little is known about the role of fire in the reproduction and establishment of savanna grassland plants. Initial studies on heat shock simulated in the laboratory suggest that fire does not break seed dormancy, stimulate germination, or kill the seeds (Le Fichino et al, 2016;, whereas in field experiments, although many seeds died, fire indirectly promoted germination of surviving seeds, by reducing vegetation cover, which increased soil surface temperature fluctuation (Daibes et al, 2017). In a laboratory study of grasses of southern Africa, Ghebrehiwot et al (2009) found that exposure to liquid smoke increased germination rates of five of six species; effects of elevated temperatures had differing effects on seedling growth, suggesting that elevated post-fire temperatures may favour establishment of some species over others.…”

Fire and legume germination in a tropical savanna: ecological and historical factors

“…Mbalo and Witkowski, 1997;Gashaw and Michelsen, 2002;Dayamba et al, 2008) and South America (e.g. Ribeiro et al, 2013;Fichino et al, 2016;Daibes et al, 2017).…”

Post‐burning germination responses of woody invaders in a fire‐prone ecosystem

“…; Daibes et al . , ). For example, the heat intensity to which seeds are exposed during a wildfire depends on seed distribution (i.e.…”