Résumé
Modern intensive agricultural systems generally focus on the productivity of monocultures. They are characterized by a low diversity of crops, with uniform and symmetrical planting layouts. They largely rely on the utilization of chemical inputs. They are widely denounced for their negative environmental impacts. In this context, the ecological intensification framework proposes the exploitation of biodiversity in order to better achieve such ecosystem services and soil conservation. Intercropping, i.e., the simultaneous growth of two or more crops mixed in the same field, appears to have the potentialities to improve the productivity, resilience capacity, and ecological sustainability of agroecosystems through the intensification of such positive interactions between plants as facilitation and niche complementarity. Cereal-legume intercropping turns out to be effective in low-N agroecosystems, since legumes have the ability to fix atmospheric nitrogen via their symbiosis with rhizobia. This fixed N, in turn, benefits the cereal through various ecological processes. The objective of the project is to improve the benefit of legumes for intercropped cereals in low-input agroecosystems through the management of plant-plant and plant-microbe interactions. The nitrogen-fixing symbiosis requires phosphorus and iron to be efficient. While these nutrients are prone to be lacking in N-limited agroecosystems, as is the case in Mediterranean agroecosystems, plant-plant interactions and rhizobacteria and mycorrhiza interactions seem to play an important role in their acquisition and efficient utilization. We propose the development of a participatory research project in four Mediterranean agroecosystems. Agronomic and environmental diagnosis will be performed in the field to assess N and P biogeochemical cycles, as well as Fe availability, in combination with the plant performances and the diversity of soil microorganisms. Molecular identification of soil microorganisms from the most productive sites will be done and research of genes for tolerance to Fe- and P-deficiencies will be realized. Glasshouse experiments involving various cultivars of cereals and legumes, as well as the previously identified microorganisms, will be done in order to disentangle the various mechanisms of nutrient acquisition, sharing, and transfer between plants. Other experiments will assess the effects of cereal-legume-microbe interactions on the development and architecture of the plant root systems and root hair development. The lines of research are integrated with a strategy of functional ecology on plant-microbe-soil interactions in the agroecosystems of Gabes (Tunisia), Boumedfaa (Algeria), Beni Mellal (Morocco), and Thessaloniki (Greece). Using multidisciplinary and innovative approaches, the program will provide novel knowledge and understanding of agroecosystem management for food production.