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AOBPreview originally published online on November 16, 2007
Annals of Botany 2008 101(1):165-173; doi:10.1093/aob/mcm287
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© The Author 2007. Published by Oxford University Press on behalf of the Annals of Botany Company. All rights reserved. For Permissions, please email: journals.permissions@oxfordjournals.org

Effect of Water Content Components on Desiccation and Recovery in Sphagnum Mosses

Tomás Hájek1,2,* and Richard P. Beckett3

1 Institute of Botany of ASCR, Dukelská 135, CZ-379 82 Trebon, Czech Republic
2 Faculty of Science, University of South Bohemia, Branisovská 31, CZ-370 05 Ceské Budejovice, Czech Republic
3 School of Biological and Conservation Sciences, University of KwaZulu Natal, Private Bag X01, Scottsville 3209, Republic of South Africa

* For correspondence. E-mail hajek{at}butbn.cas.cz

Received: 5 June 2007    Returned for revision: 15 August 2007    Accepted: 2 October 2007    Published electronically: 16 November 2007

Background and Aims: The basic parameters of water relations were measured in Sphagnum mosses. The relationships of these parameters to the photosynthetic response to desiccation and the ecology of these mosses were then tested.

Methods: The water relations parameters of six Sphagnum species (mosses typical of wet habitats) and Atrichum androgynum (a moss more typical of mesophytic conditions) were calculated from pressure–volume isotherms. Photosynthetic properties during and after moderate desiccation were monitored by chlorophyll fluorescence.

Key Results: When desiccated, the hummock-forming species S. fuscum and S. magellanicum lost more water before turgor started dropping than other sphagna inhabiting less exposed habitats (73 % compared with 56 % on average). Osmotic potentials at full turgor were similar in all species, with an average value of –1·1 MPa. Hummock sphagna had clearly more rigid cell walls than species of wet habitats ({varepsilon} = 3·55 compared with 1·93 MPa). As a result, their chlorophyllous cells lost turgor at higher relative water contents (RWCs) than species of wet habitats (0·61 compared with 0·46) and at less negative osmotic potentials (–2·28 compared with –3·00 MPa). During drying, {Phi}PSII started declining earlier in hummock species (at an RWC of 0·65 compared with 0·44), and Fv/Fm behaved similarly. Compared with other species, hummock sphagna desiccated to –20 or –40 MPa recovered more completely after rehydration. Atrichum androgynum responded to desiccation similarly to hummock sphagna, suggesting that their desiccation tolerance may have a similar physiological basis.

Conclusions: Assuming a fixed rate of desiccation, the higher water-holding capacities of hummock sphagna will allow them to continue metabolism for longer than other species. While this could be viewed as a form of ‘desiccation avoidance’, hummock species also recover faster than other species during rehydration, suggesting that they have higher inherent tolerance. This may help them to persist in drought-exposed hummocks. In contrast, species growing in wet habitats lack such strong avoidance and tolerance mechanisms. However, their turgor maintenance mechanisms, for example more elastic cell walls, enable them to continue metabolizing longer as their water contents fall to the turgor-loss point.

Key words: Sphagnum, Atrichum androgynum, mosses, desiccation, recovery, water content, turgor, wall elasticity, photosynthesis, chlorophyll fluorescence


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