Abstract :

Seed legumes are generally recognised for their many nutritional and environmental benefits. However, most of these species can be defined as orphan crops. This highlights the lack of data and knowledge about the diversity of legumes. The study of this diversity via the functional trait approach could guide the insertion of legumes in agroecosystems. The aim of this work was to synthesise current knowledge on the functional diversity of cultivated legumes at the interspecific level, as well as to generate new knowledge on the relationships between functional traits and agroecosystem functioning. We focused on a number of agro-ecosystem properties that we hypothesised to be good indicators of three important agro-ecosystem services related to food supply in low-input systems: dryland yield, nitrogen fixation and weed competitiveness. To do this, we combined methods and approaches from different disciplines: functional ecology, physiology and agronomy. We applied multivariate statistical methods to a database collected in the literature and then to original data collected during a field experiment to explore the relationships between traits and properties of agroecosystems in multiple environments (literature data) or under common and optimal environmental conditions (field experiment). An experiment under controlled conditions was also used to assess the effect of water deficit on key processes such as transpiration and biological nitrogen fixation. Our results highlighted the covariation structure as well as trade-offs between the properties supported by different legume species. Legume diversity was also described through functional traits. Leaf traits were highlighted as the main element of inter- and intra-species variability. The nitrogen content of plant organs and seeds was also an important factor in legume diversity. These traits were linked to agroecosystem properties. Although the latter can be predicted by multiple combinations of traits, it was possible to identify the LNC as an important indicator of agroecosystem properties. We compared different approaches (meta-analysis and experimental) and discussed intra-species variability. The controlled experiment revealed high intra- and interspecific variability in the response of nitrogen fixation and transpiration dynamics, as well as relationships between leaf traits, C/N metabolism and responses of growth, transpiration and N2 fixation to soil drying. We also discussed the intrinsic limitations of the trait-based approach and its potential for application in the design of diverse agroecosystems.