Journal Article

Size matters for violent discharge height and settling speed of <i>Sphagnum</i> spores: important attributes for dispersal potential

Sebastian Sundberg

in Annals of Botany

Published on behalf of The Annals of Botany Company

Volume 105, issue 2, pages 291-300
Published in print February 2010 | ISSN: 0305-7364
Published online January 2009 | e-ISSN: 1095-8290 | DOI: http://dx.doi.org/10.1093/aob/mcp288
Size matters for violent discharge height and settling speed of Sphagnum spores: important attributes for dispersal potential

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Background and Aims

Initial release height and settling speed of diaspores are biologically controlled components which are key to modelling wind dispersal. Most Sphagnum (peat moss) species have explosive spore liberation. In this study, how capsule and spore sizes affect the height to which spores are propelled were measured, and how spore size and spore number of discharged particles relate to settling speed in the aspherical Sphagnum spores.

Methods

Spore discharge and spore cloud development were filmed in a closed chamber (nine species). Measurements were taken from snapshots at three stages of cloud development. Settling speed of spores (14 species) and clusters were timed in a glass tube.

Key Results

The maximum discharge speed measured was 3·6 m s−1. Spores reached a maximum height of 20 cm (average: 15 cm) above the capsule. The cloud dimensions at all stages were related positively to capsule size (R2 = 0·58–0·65). Thus species with large shoots (because they have large capsules) have a dispersal advantage. Half of the spores were released as singles and the rest as clusters (usually two to four spores). Single spores settled at 0·84–1·86 cm s−1, about 52 % slower than expected for spherical spores with the same diameters. Settling speed displayed a positive curvilinear relationship with spore size, close to predictions by Stokes' law for spherical spores with 68 % of the actual diameters. Light-coloured spores settled slower than dark spores. Settling speed of spore clusters agrees with earlier studies. Effective spore discharge and small, slowly settling spores appear particularly important for species in forested habitats.

Conclusions

The spore discharge heights in Sphagnum are among the greatest for small, wind-dispersed propagules. The discharge heights and the slow settling of spores affect dispersal distances positively and may help to explain the wide distribution of most boreal Sphagnum species.

Keywords: Bryophyte; explosive capsules; long-distance dispersal; peatland; peat moss; settling speed; Sphagnum; spore; spore capsule; Sweden; terminal velocity; wind dispersal

Journal Article.  6957 words.  Illustrated.

Subjects: Ecology and Conservation ; Evolutionary Biology ; Plant Sciences and Forestry

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