The importance of seed mass for the tolerance to heat shocks of savanna and forest tree species

Abstract

Nomenclature Lista de Esp ecies da Flora do BrasilAbstract Questions: Does seed mass influence the tolerance of seeds to the effects of heating in fires? Is the tolerance to heat shocks during fire events dependent mostly on seed mass itself or to other traits linked to the species ecological origin, e.g. non-fire-prone (forest) and fire-prone (savanna) environments?Location: Savanna and forest ecosystems of the Cerrado biome, Brazil.Methods: Heat shocks were applied to seeds of 17 selected common tree species in savanna (ten species) or forest ecosystems (seven species) of the Cerrado biome. After being submitted to a heat shock, seeds were allowed to germinate in chambers set at 30°C. Germination percentage was calculated for each treatment and species. For comparison purposes, species were grouped into two functional groups (forest and savanna) and also into seed size classes (small, medium and large). We used generalized linear model to analyse heat shock effects on seed germination of savanna and forest tree species, and how seed size affected the germination response.Results: Seed mass influenced seed tolerance to heat shock. Larger seeds had higher survival when subjected to heat shock, independent of species' ecological origin. In addition, seeds from species occurring in fire-prone environments (savanna) were more tolerant to high levels of heat shock than seeds from species occurring in non-fire-prone environments (forest). Conclusion:In response to global climatic change, fire regimes in savannas of South America are expected to become more frequent and intense, even expanding into currently non-fire-prone environments. In this sense, our findings indicate that species from savannas (fire-prone environments) might have an adaptive advantage to these consequences of climatic changes, potentially leading to expansion of the savanna ecosystems.

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

“…This helps to explain how small-seeded shrubs could show higher seed mortality under 200 °C, despite facing frequent fires in the grassy savannas. Trees, however, usually have relatively larger seeds (Moles et al, 2005;Rubio de Casas et al, 2017), which may provide protection to the embryo (Ribeiro et al, 2015). Moreover, this trait is phylogenetically conserved (Moles et al, 2005; different establishment strategies in contrasting habitats (see Hoffmann, 2000).…”

“…Some seed traits (e.g. seed mass, seed shape, dormancy class) are predictors of seed responses to fire temperatures (Ribeiro et al, 2015;Gómez-González et al, 2016;Ramos et al, 2016;Saracino et al, 2017). For instance, larger seeds tend to show higher heat tolerance (Gashaw and Michelsen, 2002;Ribeiro et al, 2015), while smaller ones are more easily stimulated to germinate following fires (Hanley et al, 2003).…”

“…Regarding regeneration from seed, current literature suggests that savanna fires do not affect emergence from soil seed banks (de Andrade and Miranda, 2014), and heat shocks also seem to have little effect on germination of Cerrado species (Ribeiro et al, 2013;Fichino et al, 2016). However, while seeds from fire-prone grasslands and savannas are expected to be heat-tolerant (Le Stradic et al, 2015;Fichino et al, 2016), seeds from fire-free forest trees can be heat-sensitive, showing higher mortality (Ribeiro and Borghetti, 2014;Ribeiro et al, 2015). Fire could therefore be an environmental filter preventing the establishment of forest species in savannas (Hoffmann, 2000;.…”

“…Alternatively, seed traits could be the key drivers of seed mortality, depending primarily on the species' phylogenetic affiliation irrespective of vegetation type. For instance, lineages with larger and rounder seeds could better protect the embryos from heat shocks (Ribeiro et al, 2015;Gómez-González et al, 2016). Thus, we used phylogenetically controlled analyses to disentangle the ecological (i.e.…”

A 7000‐year history of changing plant trait composition in an Amazonian landscape; the role of humans and climate

“…; Rosell ), (2) large seeds have higher survival probability in fire events (Ribeiro et al . ) and have enhanced resprouting ability after fire events (Lahoreau et al . ) and (3) zoochorous genera have larger seeds (Westoby et al .…”