How does fire affect germination of grasses in the Cerrado?

Abstract

Fire is a frequent disturbance in the Cerrado and is one of the major factors affecting vegetation structure and diversity. Fire events open gaps within the herbaceous layer and increase temperature fluctuation in the soil surface. In addition to being an important environmental filter for germination, fire is a germination cue for species with physiological dormancy. This study aimed to evaluate the germination of native grasses, using daily temperature fluctuations and heat shock to overcome physiological dormancy in native grasses. We also evaluated seed longevity after dispersal for some species. We conducted the daily temperature fluctuation experiments on seeds of ten native grass species, which were collected and then placed in germination chambers simulating thermal fluctuation throughout the day (19–55°C). We also subjected seeds to different heat-shock treatments: 100°C for 1 min, 100°C for 3 min and 200°C for 1 min. To determine seed longevity, we stored seeds for 6 and 12 months after collection and then set them to germinate (27°C, 12/12 h light). Non-germinated seeds from all experiments were tested for viability. Most species had low longevity and germination percentages. Those that had physiological dormancy were stimulated to germinate when exposed to temperature fluctuations. One species resisted temperatures up to 200°C. For all other species, neither treatment affected germination percentages. Our results indicate the importance of these environmental filters for seedling recruitment of these species, considering the low longevity and the presence of physiological dormancy.

Post‐fire regeneration strategies in a frequently burned Cerrado community

“…Furthermore, around 25% of non-dormant species had low germination and viability percentages under control conditions, mainly due to a great amount of embryo-less seeds (data not shown), as has been observed for other Cerrado communities (Le Stradic et al, 2015;Dairel & Fidelis, 2020;Dayrell et al, 2017). Lamont et al (2011) argue that low fecundity among resprouting species may be due to accumulation of deleterious somatic mutations, given that resprouters live through many fire cycles and accumulation of mutant alleles and chromosomal aberration is a time-dependent process.…”

“…Fire-related seeding is often associated with synchronizing germination to a single point in time, where germination may be triggered by different fire cues, such as heat shocks (Auld & Denham, 2006;Reyes & Trabaud, 2009;Moreira et al, 2010;Moreira & Pausas, 2012), temperature fluctuations (Santana et al, 2010;Musso et al, 2015;Daibes et al, 2017;Dairel & Fidelis, 2020), and smoke (Keeley & Fotheringham, 2000;Keeley & Pausas, 2018;Zirondi, José, et al, 2019). Heat shocks caused by fire have been reported to stimulate germination in several species of fire-prone ecosystems, such as those in Australia and in the Mediterranean region, mainly in hard-seeded species in which high temperatures may break physical dormancy, thus enabling germination (Auld & O'Connell, 1991;Williams et al, 2003;Reyes & Trabaud, 2009;Moreira et al, 2010;Moreira & Pausas, 2012).…”

“…After fires, many woody and herbaceous species resprout from dormant buds (Coutinho, 1990;Medeiros & Miranda, 2008;Pausas et al, 2018;Pilon et al, 2020), but the role of post-fire seed germination as a regeneration mechanism in Cerrado remains unclear. Even though post-fire seed germination has been observed in grasslands and savannas that undergo surface fires (Overbeck & Pfadenhauer, 2007;Clarke et al, 2015;Ramos et al, 2019;Pilon et al, 2020), studies evaluating seed responses after heat shocks in the Cerrado have done so with few species (Ribeiro et al, 2013;Le Stradic et al, 2015;Fichino et al, 2016) or are restricted to certain clades (Ramos et al, 2016;Daibes et al, 2019;Zirondi, José, et al, 2019;Dairel & Fidelis, 2020), hindering the understanding of general postfire regeneration mechanisms at the community scale. Moreover, few studies addressing fire-related seed responses in the Cerrado have taken into account plant resprouting ability following experimental fires (but see Pilon et al, 2020).…”

A research agenda for the restoration of tropical and subtropical grasslands and savannas

“…Extensive knowledge gaps in basic seed biology of TGB species severely limit our capacity to use seed‐based restoration strategies. Landscape‐scale restoration requires large quantities of seeds, but many TGB herbaceous species have traits that limit seed sourcing, including: (1) small populations, individual rarity, and irregular fruiting phenology (Dayrell et al 2016); (2) low resource allocation to reproduction (Bond & Midgley 2001); (3) recalcitrant seeds in forbs that impede seed storage; (4) high seed dormancy that inhibits germination (Rusdy 2017); (5) low seed quality (low viability, high percentage of empty seeds, Dairel & Fidelis 2020; Kolb et al 2016; Dayrell et al 2017); and (6) fire‐dependent flowering, seed release, or germination (Bond 2019). Seed germination of herbaceous species is often low, slow, and asynchronous.…”

Responses of Neotropical Savannah Plant Species to Abiotic Stresses: A Structural and Functional Overview

“…As an escape strategy, many herbaceous species synchronize seed production before annual burning periods and enter a type of dormancy that only ends after high-temperature exposure [192], as reported for different plant species. For instance, the dormancy of Sporobolus cubensis (Poaceae), a herbaceous species of the Neotropical savannah, was broken by exposure to 200°C, indicating the need of fire temperature for its germination [195]. However, many seeds and underground plant organs may be protected against scorching since the heat from fire events does not reach deeper layers of the soil [196].…”