L' évaluation des caractéristiques agronomiques d'espèces prairiales par leurs traits de vie comme étape préalable au diagnostic des communautés à flore complexe :

Abstract : Technical advising in management of native meadows deal for a long time with the difficulty of stake in work of the generic methods of diagnosis based on the floristic study of plant communities. Time consuming and needing botanical expertise these methods are actually little applied by the farming consultants. An alternative method, based on the identification of dominant plant functional types (TFPs) in the meadow, allows a simple reading and diagnosis of the vegetation without appealing to botanic skills. TFPs can be define response or effect groups of species established according respectively to the response of the species towards gradients of environment factors or to their effect on the productive or environmental functions of the meadow ecosystem. Leaf traits such as Specific Leaf Area (SLA), Leaf Dry Matter Content (LDMC) and Leaf Life Span (LLS) have been proposed to identify the growth strategy of species, principally according to their use of soil available nutrients. However, their relation with the agronomic characteristics defining the value of use of the communities has not been studied. The application of this approach to riche species communities requires a preliminary study at the species level. The objective of this work is to asses the relevance of the plant traits (particularly the leaf traits) to classify the species according to their phenology, their nutritive value and their growth. In this purpose, at the INRA research centre of Auzeville, Toulouse mini plots of pure stands of 37 species (21 grasses and 16 dicotyledonous which 3 legumes) were sowed in a 3 replicates split-split plot design in which the species and the level of N availability were respectively the principal and the secondary factors. N treatments were considered as levels of N availability limiting or not limiting the grass growth. Levels of phosphorous, potassium and water were not limiting during the experimental time. Contrarily to SLA and LLS, the LDMC allows separating grasses from the others species. Values of LDMC and SLA vary according to the periods of measures. These same traits and the LLS vary in response to the availability in nitrogen. In spite of the temporal variability and the plasticity of trait values in response to N availability, the rank of the species remained similar for every of three leaf traits characterizing the strategies of growth. These observations were also observed when the analysis was only done on the grass populations. As regards the phenology of the species, the classification established by the LDMC was closer to that established by the flowering stage, the seed ripening stage and principally the start of the stem elongation. The comparative study of grass growth under not limiting conditions confirmed an efficiency of conversion of the radiation significantly higher in species having a resource capture strategy. These species show an earlier development of the leaf area index, higher values of the digestibility of the organic matter, lower contents in fibbers and its components, shorter LLS and an earlier phenology. A discussion on the possibility to extent this specific approach at the level of the community is done. The only knowledge of the LDMC of grasses populations (measured or provided by a traits data-base) inform about the phenology, the growth and the nutritive value of the community an it could be used to asses meadow and grassland value of uses
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Raouda Al Haj Khaled. L' évaluation des caractéristiques agronomiques d'espèces prairiales par leurs traits de vie comme étape préalable au diagnostic des communautés à flore complexe :. Autre. Institut National Polytechnique de Lorraine, 2005. Français. ⟨NNT : 2005INPL080N⟩. ⟨tel-01752539⟩

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