Sur l'organisation phytochimique de formations prairiales permanentes

Abstract

Organic and mineral components have been analysed on 18 dicotyledonous species of permanent grassland communities. Multivariate analysis revealed an opposition between a macromolecular pool (cellulose and lignin) and a nutrient pool (potassium and phosphorus, nitrogen). The first pole is characterized by Tragopogon pratensis L. (Compositae) and Galium mollugo L. (Rubiaceae), the second by Anthriscus sylvestris (L.) Hoffm. (Umbelliferae) and Geranium sylvaticum L. (Geraniaceae). The most thermo-helio-xerophilous species (Knautia arvensis (L.) Coult and Tragopogon pratensis) belong to the first group, whereas the second group includes the cool-environment species (like Alchemilla xanthochlora Roth.), which reveals an ecophysiological determinism. Moreover, correlations between the biochemical and ecological structure, and other interrelated parameters, including sclerophylly, have been shown. Compared to lignous and sempervirent plant communities, the grassland species have lower phenolic and lignin contents but higher glucide and nutrient (potassium and phosphorus) contents, which is in accordance with their food value. For this herbaceous community, the C/N ratio indicates the same general equilibrium between cell-wall macromolecules and nitrogen than for two other plant communities (mainly ligneous) previously studied, with some differences revealing distinct trends from the same general metabolic sheme.Key words: dicotyledonous plant communities, biochemical organization, C/N ratio, ecophysiology.