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Accueil du site → Doctorat → Pays-Bas → < 2000 → The ecology of Ruppia drepanensis Tineo in a Mediterranean brackish marsh (Donana National Park, SW Spain) : a basis for the management of semiarid floodplain wetlands

Wageningen Universiteit (1995)

The ecology of Ruppia drepanensis Tineo in a Mediterranean brackish marsh (Donana National Park, SW Spain) : a basis for the management of semiarid floodplain wetlands

Santamaria Galdon, L.E.

Titre : The ecology of Ruppia drepanensis Tineo in a Mediterranean brackish marsh (Donana National Park, SW Spain) : a basis for the management of semiarid floodplain wetlands

Auteur : Santamaria Galdon, L.E.

Université de soutenance : Wageningen Universiteit

Grade : PhD thesis 1995

Résumé
One of the most important features of floodplain wetlands, both from an economical and a purely naturalistic point of view, is their high secondary production, with abundant invertebrates, fish and birds. This production is primarily based on the high productivity of aquatic macrophytes and their associated periphytic algae. Semi-arid floodplain wetlands have a very dynamic character, with yearly recolonization by the fauna and flora as a characteristic phenomenon. It is a consequence of the annual cycle of inundation and subsequent desiccation. The present study concentrates on the understanding of the dynamics of the aquatic vegetation as a research strategy for the management of such wetlands. Aims of the study were to identify potential causes for the decline of the submerged macrophyte populations, and to better understand the factors behind the interannual variation in their development. The marsh of the Doñana National Park (SW Spain) was selected as a study area. The research concentrated on the growth, photosynthetic performance and reproduction of the dominant macrophyte species in the brackish area of the marsh, Ruppia drepanensis Tineo. Working hypotheses were generated from a conceptual model explaining the life cycle and biomass development of the submerged macrophyte populations. In this model, we consider the light climate as the main factor limiting the development of the submerged vegetation. High nutrient concentration is hypothesized as the main factor triggering the decline of the submerged macrophytes, either by a indirect shading effect due to increased growth of periphyton, or by a direct physiological effect on the plant development (toxicity of ammonia) and reproduction (delay of the flowering event caused by high nitrogen availability).

Light intensity and temperature strongly influenced growth and reproduction. The plants showed a strong capacity for photosynthetic acclimation to low light intensities. A weaker acclimation capacity was coupled with a high plasticity with respect to the temperature effect on photosynthesis.

Photoperiod and photosynthetic period did not influence growth, but affected reproduction. A longer photoperiod resulted in earlier flowering, and a longer photosynthetically active period resulted in more flowering and eventually higher seed production. Flowering was triggered by temperatures above 15 °C, and was strongly reduced at 30 °C. Although in all cases some plants were able to flower, the set of characteristics necessary for a successful reproduction can be defined as a long photosynthetic photoperiod and a range of temperatures above 15 °C but below 30 °C.

Mots clés : potamogetonaceae / plant ecology / plant communities / aquatic communities / marshes / wetlands / polders / brackish water / spain

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