Evidence for direct effects of fire‐cues on germination of some perennial forbs common in grassy ecosystems

Abstract

In grassy ecosystems of south-eastern Australia, fire maintains richness of native forbs. It is commonly thought that fire promotes regeneration indirectly by reducing competition for light and providing gaps for recruitment, rather than directly stimulating germination. However, physiological dormancy and morphophysiological dormancy are common, and few studies have explored responses to fire-cues among dormant or hard-to-germinate forbs. Recent studies from other fire-prone ecosystems suggest that in some cases, fire-cues may not alleviate physiological or morphophysiological dormancy, but instead promote germination in combination with treatments which alleviate dormancy. We experimentally tested the prevailing hypothesis that perennial forbs common in south-eastern Australian grassy ecosystems do not germinate in direct response to fire. Responses to fire-cues both inherently and in combination with treatments which alleviate dormancy were investigated for seven species. Two fire-cues (smoke and heat) plus a treatment of both heat + smoke were applied to fresh seed at three temperatures (35/25°C, 30/20°C and 25/15°C). Following this, the effect of fire-cues on seed that had undergone warm stratification, cold stratification and dry-afterripening was investigated. Three species -Arthropodium strictum, Cheiranthera cyanea and Dianella revoluta responded to fire-cues inherently, although germination in C. cyanea was low. High germination of D. revoluta was found when fire-cues were combined with warm stratification. Fire-cues had no effect on germination of Brunonia australis, Burchardia umbellata and Eryngium ovinum. Germination of Stypandra glauca was zero following all treatment combinations. Our finding that fire-cues promote germination of three of the seven study species did not provide sufficient evidence to reject the current hypothesis that germination of perennial forbs is not typically promoted by fire-cues. However, this study highlights the important direct role fire-cues can play in promoting germination of some perennial forbs both inherently and in combination with treatments used to alleviate physiological dormancy.Total seed collected is the amount of seed from each population that was pooled to create the regional mix used in experiments. '-' = population size unknown.

Fire Seasonality, Seasonal Temperature Cues, Dormancy Cycling, and Moisture Availability Mediate Post-fire Germination of Species With Physiological Dormancy

“…The important role that seasonal temperature cues play in regulating fire-stimulated germination of many PD species has been recognized only relatively recently ( Ooi et al, 2006 ; Mackenzie et al, 2016 ; Collette and Ooi, 2017 , 2020 ; Hodges et al, 2019 ). Very few studies have investigated the effect of fire-related germination cues such as heat and smoke in combination with a full complement of seasonal temperatures, limiting our understanding of the germination ecology of PD species in temperate fire-prone regions and predictions of the impacts of altered fire regimes on recruitment.…”

Land‐use legacies limit the effectiveness of switches in disturbance type to restore endangered grasslands

“…The common disturbances reviewed in this study are likely to have similar (albeit not synonymous) effects on microsite conditions via the removal of biomass. For many grassland species, fire‐related germination cues (such as smoke and heat) promote germination (Vening et al 2017; Carthey et al 2018; Hodges et al 2019). For such species, substituting grazing and mowing for fire is unlikely to promote germination.…”

“…If there is a legacy of the past management, grazing may have eliminated grazing‐sensitive native species and there may be very few native species that can then take advantage of a new regime; they have been lost from the species pool. Further, it is unclear if grassland species rely on fire to maximize germination through effects of heat and smoke, or if fire promotes recruitment by reducing light limitation, and hence whether fire is substitutable (Hodges et al 2019; Price et al 2019). It remains unclear if changes in disturbance type can enhance conservation outcomes, by promoting native species that are currently suppressed or disadvantaged, while simultaneously reducing exotic plant cover and richness.…”

Predictability of Biotic Stress Structures Plant Defence Evolution

“…Altered photoperiod induces stress in Arabidopsis thaliana [77] Temperature Heat stress alters shock-factor-responsive gene expression in Arabidopsis thaliana [78] Rapid and gradual decreases in temperature trigger different pathways in Arabidopsis thaliana [79] Fire induced heat alleviates dormancy across grassland species in South-Eastern Australia [80] Salinity Salinity reduces the capacity of the photosynthetic system in cabbage (Brassica oleracea)…”