Global environmental changes, particularly climate change, requires to rethink crop management practices to reduce fertilizer and pesticide inputs. This leads to greater heterogeneity within the canopy and a larger dependency on environmental constraints. For example, lowering crop densities and synthetic input rates will increase variability in plants biomass, favor weed development as well as that of pathogens and parasites, which are potential sources of crop damage. Agroecology promotes the self-regulatory capacities of ecosystems based on biological processes through for instance an increase in biodiversity within the crop (a bio-diverse canopy). These processes remain poorly understood and little quantified in agroecosystems, and therefore new references need to be established. In this context Eco&Phy has recently started studying biological regulations within agroecosystems (root exudates, secondary metabolism, quality of light), and broaden the range of studied crops (pure crops, varietal mixtures, species associations, interactions with macro fauna). In this five-year RP, our ambition is to unravel key regulatory processes and assess their share in the resilience of canopy. The outcomes of this project aim at identifying key biological regulation processes and the relevant scales to design resilient agroecosystems.

The project will consist of three components, based on the two crop species mainly studied in the team (wheat and oilseed rape), grown in pure crops, in varietal mixtures (wheat), or as intercrops (oilseed rape/legumes) depending on the processes studied and the objectives. The first two components will address the two themes already addressed in the team enriched with biological regulatory processes to assess their contribution: (i) plant defense processes (plant- pest interactions) and (ii) carbon and nitrogen resource management. A third, more exploratory component (iii) will focus on the role of communication processes, which we assume will be important in understanding the functioning of agroecosystems.

• Biological regulations in plant defense processes. The aim will be to assess virulence transmission in a pathogen population during a growing season in wheat varietal mixtures, and identify biological regulations induced by the mixture. This component is the subject of a thesis project in collaboration with the BIOGER unit.
• Biological regulations in the management of N and C resources considering within-crop diversity of organisms. The aim will be to (i) better understand the management of C and N resources in oilseed rape-legume associated covers by identifying key biological regulation processes (competition and facilitation at aerial and root levels, plasticity of aerial and root architectures, light effect and signals). Additionally, we will (ii) evaluate the role of plants-microbial interactions in the C and N cycles, and especially the role of root exudates in the C balance, and of the microbial compartment in N supply to the crop. This component will be supported by IMPULSE, RAPSODYN, BREEDWHEAT projects.
• Exploring the role of communication in biological regulations. Example of VOC in plant-pest interactions. We will develop prospective researches on the role of VOCs in plant-plant-pest interactions, by both identifying the compounds involved and understanding their role in the ecosystem resilience. It relies on the team's dual expertise measuring VOC emitted by plants by PTR-QiTOFMS and designing controlled mesocosm devices for the control and differential removal of plant organs in stands under stress (PERISCOPE, LED, PhAIRE). Tri- trophic relations between plants, aggressors and auxiliaries, will be studied in the case of push-pull systems (in oilseed rape), which has rarely been evaluated in our latitudes (collaboration with BIOGER and Agronomie units).

This RP will be jointly carried out at ECOSYS level within the "Biomasses" structuring theme (C-N cycles, soil-plant interactions) and the "Diversity” theme (heterogeneous cover, plant-pest interactions).