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Ann Bot. Dec 2008; 102(6): 989–996.
Published online Oct 14, 2008. doi:  10.1093/aob/mcn190
PMCID: PMC2712407
Clonal Plasticity of Aquatic Plant Species Submitted to Mechanical Stress: Escape versus Resistance Strategy
Sara Puijalon,1,2* Tjeerd J. Bouma,2 Jan Van Groenendael,3 and Gudrun Bornette1
1UMR CNRS 5023, ‘Ecology of Fluvial Hydrosystems’, Université Lyon 1, 43 Boulevard du 11 novembre 1918, F-69622 Villeurbanne Cedex, France
2Netherlands Institute of Ecology (NIOO-KNAW), Centre for Estuarine and Marine Ecology, PO Box 140, 4400 AC Yerseke, The Netherlands
3Institute of Water and Wetland Research, Department of Ecology, Section of Aquatic Ecology and Environmental Biology, Radboud University Nijmegen, Toernooiveld, 6525 ED Nijmegen, The Netherlands
*For correspondence. E-mail puijalon/at/gmail.com
Received February 27, 2008; Revised April 14, 2008; Accepted August 22, 2008.
Abstract
Background and Aims
The plastic alterations of clonal architecture are likely to have functional consequences, as they affect the spatial distribution of ramets over patchy environments. However, little is known about the effect of mechanical stresses on the clonal growth. The aim of the present study was to investigate the clonal plasticity induced by mechanical stress consisting of continuous water current encountered by aquatic plants. More particularly, the aim was to test the capacity of the plants to escape this stress through clonal plastic responses.
Methods
The transplantation of ramets of the same clone in two contrasting flow velocity conditions was carried out for two species (Potamogeton coloratus and Mentha aquatica) which have contrasting clonal growth forms. Relative allocation to clonal growth, to creeping stems in the clonal biomass, number and total length of creeping stems, spacer length and main creeping stem direction were measured.
Key Results
For P. coloratus, plants exposed to water current displayed increased total length of creeping stems, increased relative allocation to creeping stems within the clonal dry mass and increased spacer length. For M. aquatica, plants exposed to current displayed increased number and total length of creeping stems. Exposure to current induced for both species a significant increase of the proportion of creeping stems in the downstream direction to the detriment of creeping stems perpendicular to flow.
Conclusions
This study demonstrates that mechanical stress from current flow induced plastic variation in clonal traits for both species. The responses of P. coloratus could lead to an escape strategy, with low benefits with respect to sheltering and anchorage. The responses of M. aquatica that may result in a denser canopy and enhancement of anchorage efficiency could lead to a resistance strategy.
Key words: Phenotypic plasticity, morphology, submerged aquatic vegetation, clonality, clonal architecture, Potamogeton coloratus, Mentha aquatica, escape, resistance, mechanical stress, thigmomorphogenesis
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