Comparative effects of desiccation, heat shock and high temperatures on seed germination of savanna and forest tree species

Abstract

Although forest and savanna biomes predominate in tropics regions, the factors that control their distribution remain unclear. South American savannas occur in regions that are considered warm and humid enough to support forests, indicating that agents other than climate determine the occurrence of one or the other physiognomy. Herbivory, fire and water deficit have been considered environmental filters that limit the forest species encroachment in savanna physiognomies, but the effects of these filters on the capability of these species to recruit from seeds remain poorly understood. In this study we investigated how stress factors characteristic of savanna environments, such as soil desiccation, heat shocks and high temperatures affect the survival and germination of seeds from savanna and forest tree species. We found that desiccation (to 5%) reduced the germination percentage of forest seeds, but had no effect on the germination of savanna seeds. Forest seeds were less tolerant to heat shocks of 140°C and 200°C, and showed lower germination percentage at temperatures of 35 and 40°C, when compared with savanna seeds. Savanna seeds presented longer germination times and higher germination variance than forest seeds, indicating a risk-spreading germination strategy among savanna species. The low tolerance of forest seeds to desiccation, heat shock and high temperatures may explain the low recruitment of forest trees into savanna physiognomies. Climate change models predict lower soil moisture, higher temperatures and higher fires frequency for South America biomes. Our results suggest that savanna species are likely to be more capable of withstanding the effects of these changes than forest species. METHODS Study areaSeeds were collected at the IBGE (Brazilian Institute for Geography and Statistics) Ecological Reserve (15°55′-15°58′S, 47°52′-47°55′W) and at the adjacent experimental farm Fazenda Água Limpa (FAL) (15°56′-15°59′S, 47°55′-47°58′W), both located near Brasília, DF, Brazil, at 268 L. C. RIBEIRO AND F. BORGHETTI

To resist or to germinate? The effect of fire on legume seeds in Brazilian subtropical grasslands

“…Those results are very consistently with what has been reported to some grass species from the Brazilian subtropical grasslands (Overbeck et al 2006) and herbaceous species in the Cerrado ecosystem (Fichino et al 2012;2016;Le Stradic et al 2015). When species from Cerrado were compared to forest species, the exposure to high temperatures did not affect negatively the Cerrado species, while forest species showed lower germination percentages (Ribeiro et al 2013;Ribeiro & Borghetti 2014). Therefore, even with no evidence of fire-related cues to germination, seeds can resist the passage of fire and this trait (fire resistance) should also be considered as an important trait in flammable ecosystems (Fichino et al 2016).…”

Key factors affecting seed germination of Copaifera langsdorffii, a Neotropical tree

“…The Cerrado is an environment in which fire has been a recurrent factor for thousands of years (Salgado-Laboriau et al 1997). In fact, recent studies have shown that seeds of plants of the Cerrado tend to be more tolerant to high temperatures than seeds of forest plants (Ribeiro et al 2013;Ribeiro & Borghetti 2014). Despite these recent efforts, studies assessing the effects of fire on the germination of native Cerrado plant species remain scarce, especially investigations involving species that are not endemic to this biome.…”

Intraspecific variation in seed size and light intensity affect seed germination and initial seedling growth of a tropical shrub

“…age, photoblastism, dormancy) attributes of seeds can interact with ecological variables (e.g. light, temperature, moisture, soil quality, seed predation) to determine the local abundance of plant species (Rojas-Aréchiga et al 2013;Ribeiro & Borghetti 2014;Souza & Fagundes 2017). Th us, fi nding a predictable relationship between plant life history and environmental variables will help determine the ability of plants to become established and elucidate traits that allow species to become dominant in specifi c habitats (Murray et al 2005;Ferreras et al 2015;Jelbert et al 2015).…”