Original paper

Phenology and phenotypic variation of genetically uniform populations of Elodea nuttallii (Planch.) H. St John at sites of different trophic states

Nino, F. Di; Thiébaut, G.; Muller, S.

Abstract

The morphological variation of E. nuttallii (Planch.) H. St John, a clonal aquatic macrophyte introduced in Europe, was investigated along a eutrophication gradient in a Northern Vosges stream (NE France). Studies of morphological plasticity in clonal plants have analysed responses to habitat quality in terms of spacer length and branching intensity. The capacity for these parameters to respond to environmental quality has been interpreted as an expression of foraging behaviour, as it confers the potential to intensify the placement of ramets in the more favourable patches of a heterogeneous environment. In our study, the first step consisted in testing the Foraging Concept applied to plant morphology as an adaptation to the acquisition of resources (De Kroon & Hutchings 1995). Eight morphological traits of individuals of E. nuttallii were studied monthly at three sites to document morphological plasticity according to a trophic gradient. A signifi cant difference in morphological traits appeared among the dates and among the sites. A seasonal pattern of the growth of E. nuttallii was established. In agreement with the prediction of the foraging hypothesis, there was a difference in internode and in photosynthetic surface among sites. Plants growing in oligotrophic water were long and thin, while plants growing in mesotrophic water were shorter and more robust, with a greater leaf surface. The second step consisted in investigating the degree of genetic diversity among Elodea nuttallii plants in Northern Vosges streams by analysing twenty-seven samples using Amplifi ed Fragment Length Polymorphic (AFLP) markers. Altogether 258 AFLP markers were scored using 5 primer pairs. The average proportion of shared AFLP fragments was higher than 99.80 %. These results establish that E. nuttallii propagates clonally in Northern Vosges streams. They exclude morphological variations due to the presence of ecotypes, and show an only phenotypic adaptation.

Keywords

morphological plasticityelodea nuttalliiaflpclonal plantsforaging concept