Journal Article

Clarifying the role of fire heat and daily temperature fluctuations as germination cues for Mediterranean Basin obligate seeders

Victor M. Santana, M. Jaime Baeza and M. Carmen Blanes

in Annals of Botany

Published on behalf of The Annals of Botany Company

Volume 111, issue 1, pages 127-134
Published in print January 2013 | ISSN: 0305-7364
Published online November 2012 | e-ISSN: 1095-8290 | DOI: http://dx.doi.org/10.1093/aob/mcs238
Clarifying the role of fire heat and daily temperature fluctuations as germination cues for Mediterranean Basin obligate seeders

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Background and Aims

This study aims to determine the role that both direct effects of fire and subsequent daily temperature fluctuations play in the seed bank dynamics of obligate seeders from the Mediterranean Basin. The short yet high soil temperatures experienced due to passage of fire are conflated with the lower, but longer, temperatures experienced by daily fluctuations which occur after removing vegetation. These germination cues are able to break seed dormancy, but it is difficult to assess their specific level of influence because they occur consecutively after summer fires, just before the flush of germination in the wet season (autumn).

Methods

By applying experimental fires, seed treatments were imposed that combined fire exposure/non-fire exposure with exposure to microhabitats under a gradient of disturbance (i.e. gaps opened by fire, mechanical brushing and intact vegetation). The seeds used were representative of the main families of obligate seeders (Ulex parviflorus, Cistus albidus and Rosmarinus officinalis). Specifically, an assessment was made of (1) the proportion of seeds killed by fire, (2) seedling emergence under field conditions and (3) seeds which remained ungerminated in soil.

Key Results

For the three species studied, the factors that most influenced seedling emergence and seeds remaining ungerminated were microhabitats with higher temperature fluctuations after fire (gaps opened by fire and brushing treatments). The direct effect of fire decreased the seedling emergence of U. parviflorus and reduced the proportion of seeds of R. officinalis remaining ungerminated.

Conclusions

The relevance of depleting vegetation (and subsequent daily temperature fluctuation in summer) suggests that studies focusing on lower temperature thresholds for breaking seed dormancy are required. This fact also supports the hypothesis that the seeding capacity in Mediterranean Basin obligate seeders may have evolved as a response to a wide range of disturbances, and not exclusively to fire.

Keywords: Adaptation; Cistus albidus; exaptation; fire-adaptative trait; fire heat; post-fire germination; Rosmarinus officinalis; seed bank dynamics; seedling emergence; temperature fluctuation; Ulex parviflorus

Journal Article.  5887 words.  Illustrated.

Subjects: Plant Ecology ; Plant Physiology

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