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Contrasted effects of water limitation on leaf functions and growth of two emergent co-occurring plant species, Cladium mariscus andPhragmites australis
Saltmarsh, A.; Mauchamp, A.; Rambal, S. (2006). Contrasted effects of water limitation on leaf functions and growth of two emergent co-occurring plant species, Cladium mariscus andPhragmites australis. Aquat. Bot. 84(3): 191-198. dx.doi.org/10.1016/j.aquabot.2005.09.010
In: Aquatic Botany. Elsevier Science: Tokyo; Oxford; New York; London; Amsterdam. ISSN 0304-3770, more
Peer reviewed article  

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Keywords
    Fluorescence; Photosynthesis; Water stress; Wetlands; Fresh water

Authors  Top 
  • Saltmarsh, A.
  • Mauchamp, A.
  • Rambal, S.

Abstract
    Phragmites australis tolerates a wider range of ecological conditions than Cladium mariscus and thus may be better adapted to disturbance resulting from human manipulations. We hypothesised that the difference in ecological conditions was related to differences in photosynthetic ability under water stress. We compared the reactions of the two species to water deficit related to the summer drawdown in the Mediterranean regions that may be enhanced by drainage for human activities. Stress tolerance was evaluated in a pot experiment measuring pigment contents, chlorophyll fluorescence and gas exchanges, growth rates, living and dead biomass, for plants grown in waterlogged conditions or submitted to permanent or temporary drainage. Reed was favoured by the first days of drainage with an increase in CO2 assimilation by approximately 5 μmol m−2 s−1 and an increase of the elongation rates from 1 to 1.5 cm d−1, indicating waterlogged conditions were not optimal for this species. While pigment content showed no significant effects, growth rate, percentage live above-ground biomass, chlorophyll fluorescence and net rate of CO2 assimilation declined significantly for both species from days 5 to 7 after drying started. Assimilation rates reached 2.3 and 0.3 μmol m−2 s−1 on day 9 for sawsedge and reed, respectively. Sawsedge had a 50% greater assimilation rate in the waterlogged conditions, but its responses to water loss in terms of declining growth rate and CO2 assimilation started on day 5 versus 7 for reed. By contrast, the condition of PSII as indicated by chlorophyll fluorescence was affected more in reed. Both growth rates and rates of CO2 assimilation had completely recovered for both species within 3 days of re-wetting. Our results reflect the evergreen character of sawsedge leaves that are hardly damaged by stress but decrease their activity. Reed leaves die upon excessive stress and plants may shed leaf as an adjustment to stress. Sawsedge photosynthesis will be optimal in waterlogged conditions whereas that of reed will be constant within a broad range from slightly drained to mild stress. Those responses to drainage at the leaf scale may partly explain the difference in habitat where both species are usually found.

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