Reproductive strategies may explain plant tolerance to flooding: a mesocosm experiment using six marsh species.

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إنجليزي. We investigated the impact of inundation duration on sexual and asexual reproduction strategies in six hygrophilic angiosperm species (2 annuals - Ranunculus sardous and Ranunculus ophioglossifolius, 2 rhizomatous - Juncus articulatus and Eleocharis palustris, and 2 stoloniferous species - Glyceria fluitans and Agrostis stolonifera). Plant growth during three inundation durations (natural, +3 weeks, +6 weeks) was assessed in 20 mesocosms. Biomass and reproductive traits were measured at the onset of flowering and at seed set. The six species maintained or increased their total mass in response to increased inundation period, suggesting a good tolerance to inundation stress. No changes were recorded in flowering time for the five species that flowered. The two annual species increased the number of flowers and mass allocated to sexual reproduction with increased duration of inundation, promoting extensive seed production. The response was species-specific in perennial species with an either a positive or a negative Gaussian curve of both traits in response to the increased duration of inundation. The duration of inundation affected ramet production in all perennial species except A. stolonifera, promoting ramet production in two out of the three species. In all species except E. palustris, the length and number of stolons or rhizomes were maintained, suggesting the importance of these connections in the resistance of perennial plants to flooding stress. These species occurring in repeatedly inundated habitats thus appeared to be tolerant to long inundations thanks to both sexual reproduction and vegetative propagation.