Context

In the context of global changes and with the need to reduce agricultural synthetic inputs (fertilizers, pesticides, etc.) and their impact on the environment, agroecology is an emerging opportunity. It aims at mobilizing the interactions between organisms in agroecosystems and the landscape by increasing spatio-temporal heterogeneity. This will help in promoting self-regulating processes and in reducing the need for synthetic inputs. For example, it aims to improve soil quality and thus reduces fertilizers needs, or to regulate pests with no (or few) pesticides by mobilizing biological regulations at the field and landscape scales.

Our main objective in this structuring theme is to understand which diversity (natural and cultivated) promotes positive interactions for the agroecosystem, what are the interactions, feedbacks, and at what spatial and temporal scales do they occur? For this, we will develop a systemic and ecological view of the agroecosystem. We aim at determining which heterogeneity (types, scales…) should be promoted in agroecosystems to significantly reduce the dependence on agricultural inputs, to limit their effects on the environment, and to increase the sustainability and resilience of farming systems.

Scientific questions and objectives

We will study the links between biodiversity, heterogeneity, and the functioning of biotic and abiotic components in the agroecosystem. We aim at studying the agroecosystem functioning « as a whole », by taking into account both biotic and abiotic factors at different scales of space and time. We consider two levers to optimize the natural regulations and ecological functions of the agroecosystem: intra-field diversity (e.g. cultivated biodiversity, multicropping), and landscape heterogeneity (e.g. crops and semi-natural elements diversity in the landscape, landscape structure…). We will focus on both the agricultural growing season as it is a key scale for annual production and on longer scales, which are crucial for the establishment of regulations and organisms’ evolution

The structuring theme is divided into two complementary exploration paths:

1)     An analytical study of the processes and their interactions occurring in crop heterogeneous populations at relatively fine scales, ranging from the organ to the plant. In this approach we seek to explain how the positive and negative interactions between agricultural practices, cultivated species (or varieties), and other biotic components determine production functions (acquisition and sharing of resources) and/or pest defense functions. Such an approach should ensure the identification of services associated with a intra-field crop diversity that allow for reducing synthetic inputs while increasing the resilience of the system.

2)     A spatio-temporal integrative approach of the interactions in the agroecosystem, with the aim of understanding if and how the diversity and the spatio-temporal structure of the landscape can be used as a lever to limit inputs and their impact on the agroecosystem. This includes processes studied at the field scale (1), but also processes taking place at larger scales (organisms dispersal, volatilization, genetic variability, crops diversity and structure…).

One challenge of this structuring theme is to combine these two approaches, with a back and forth action between studies acquiring knowledge at the diversified field level and studies exploring resilience possibilities at the structured landscape scale. The concepts and approaches used include plant ecophysiology, epidemiology, biophysics and environmental chemistry, ecotoxicology, evolution, evolutionary ecology, and landscape ecology.

The main questions we seek to answer are:

• By what mechanisms and to what extent intra-field cultivated biodiversity allows input reductions? Does cultivated biodiversity help to limit our needs for inputs? How does cultivated biodiversity condition access to aerial and groundwater resources (based on functional types)? How does this biodiversity impact epidemics and their damages? What is the effect of this biodiversity on the competition and facilitation phenomena within fields and in fine on their resilience to abiotic (water, nitrogen) and biotic (pest) stresses?
• How does the diversity of the agroecosystem influence the interactions between its biotic and abiotic components and therefore how does it affect the associated functionalities? For example, how a diversity of practices (e.g. fertilization practices) will impact on the one hand the epidemics, and on the other hand GES emissions in the diversified agroecosystem? What are the effects of non-cropped diversity on the functioning of the agroecosystem and vice versa?
• How will pathogens and plants evolve (or other organisms) in the face of this diversity changes, and how will they adapt to climate change? These are central questions to assess the sustainability and resilience of the studied scenarios.
• Can we use the spatiotemporal heterogeneity of the landscape as a lever to limit inputs and their impact on the agroecosystem? This question focuses on both cultivated and natural biodiversity, and on the effects of landscape heterogeneity on the biotic populations of the agroecosystem. For example, we aim at understanding the exposure determinants of living organisms (e.g. carabids) to pesticides, taking into account the fate of pesticides in landscape features and animal habitat preferences.
• How to develop an integrated approach to understand and to model the functioning of the agroecosystem at the landscape scale "as a whole", taking into account both biotic and abiotic factors in a perspective of increasing agroecosystem resilience? This will probably induce a need of simplification of the different sub- modules simulating the different organisms and components of the agroecosystem, with a focus on taking into account their interactions and feedbacks.

Regarding methodological aspects, this structuring theme raises interesting challenges. At the experimental level, it raises issues relating to the diversity we need to study: which variables should we characterize? In which compartments and at which scales (e.g. plant, field, soil, landscape)? What tools are available or need to be acquired? Are there aggregated indicators to define? Another experimental key question is how to set up long-term and landscape-scale experiments? We will try to share our skills and to apply them to the different compartments and components of the agroecosystem, and to design new experiments on diversified systems at different scales.

Regarding modeling, we are working on the development of modeling frameworks to integrate the diversity, and the associated biotic and abiotic features, at different spatial scales. We can already rely on several models developed in the lab. One challenge could be to enable dialogue between the models at the field level and the more integrative landscape-level models.

Insertion within ECOSYS and collaborations

In the perspective of a systemic vision of the agroecosystem, the different components (e.g. soil, plant, air, pests) are studied together with interactions at the intra-field scale and at the landscape scale. Therefore, the three teams of ECOSYS are involved in this structuring theme and share the scientific questions. Each of the teams provides specific skills and methods that will enrich the work developed. The contribution of the three teams is based on in situ monitoring, experimentation and modeling. Current experiments are conducted at different spatial scales: from semi- controlled devices such as mesocosmes (fine analysis of the processes and interactions related to diversity), to field (effect of cultivated biodiversity on epidemics) and landscape studies (effect of crop diversity on biotic populations). Regarding modeling, biotic populations and their interactions with abiotic features are modeled from the canopy scale to the landscape scale. The different temporal scales considered offer the opportunity to develop multi-criteria optimization approaches by simultaneously characterizing a set of functions of the agroecosystem, and to test different scenarios of practices and landscape heterogeneity.

The studies carried out may be based on models currently developed in the unit. These include models simulating host- pathogen interactions at the field and landscape scales (Septo3D, Epi3D, NitroEpidemic), models simulating the CN plants functioning and the plasticity of the architecture (e.g. ADEL-wheat, ARNICA, RGLD), and models simulating exchanges of energy, contaminating compounds (ozone, ammonia, pesticides) or non-contaminating compounds (water, CO2) (e.g. Modde, SurfAtm, VoltAir). At the field scale, current modeling work is based on the Functional-structural plant models - FSPM. One objective is to introduce in these models more biological and ecological processes to make them more able to simulate the functioning of heterogeneous stands. At the landscape scale, we rely on models such as Nitroscape or the MIPP tool, which simulate abiotic flows in agricultural landscapes. All the models described above, which are rather dedicated to one or two components of the agroecosystem, may fuel more integrative models including both biotic and abiotic features at different spatio-temporal scales.

This theme is connected with the other structuring theme. Links with the « contaminants » and « climate » themes are important to allow a broader assessment of the diverse systems we will be working on. The tools developed in the « contaminants » theme could allow to evaluate how diversification of the agricultural systems impacts pollutants fate in the different compartments of the agroecosystem. The tools developed in the « climate » theme will allow to assess whether the diversification of the systems can participate in the mitigation with regard to climate change. The « biomass »  theme  can  be  source  of  proposals  regarding the  diversity  of  practices  and  their  spatial  landscape organization we can consider. The tools developed in the other structuring themes will allow us to test the impacts of crop diversification and spatial heterogeneity at the landscape scale. However, most of the tools do not include intra- field diversity, which is undoubtedly an interesting perspective of development between the different structuring themes. Common field or landscape experiments will also be a valuable tool for strengthening connections between structuring themes.

The animation of this structuring theme will be based on scientific projects linking the three disciplinary teams of ECOSYS. Ongoing collaborations around research projects or experimental devices will be a basis for the animation. Projects include the PING project, conducted on the ZAPVS long term ecological research (LTER) site, in which we experimentally study the links between landscape structure, agricultural practices, development of epidemics, pesticides fate in rainwater and air, and exposure of non-target organisms to pesticides. Another structuring project is the inter-lab project IMPULSE, which deals with the modeling of interactions between aerial and underground biodiversity on grassland systems and field rapeseed-legume associations. Finally, some PhD projects also contribute, such as a project in collaboration with the BIOGER unit which focus on the dynamics of pathogen resistance in varietal associations of wheat, and a collaboration with the ESE unit on the role of the semi-natural elements in pests regulation at the landscape scale. Several challenges remain open, such as the development of an integrative modeling framework at the landscape scale with the integration of biotic and abiotic processes that take place at different scales of space and time. Developing such a framework is an opportunity for scientific animation. One of the objectives of the animation will also be to strengthen and develop partnerships with neighboring units (Agronomy, SADAPT, BIOGER, EcoPub, MIA Jouy ..), units of the FIRE federation (Metis, HBAN) and of the LabEx BASC (LSCE, ESE), which are all essential partners for understanding the issue of diversity in agroecosystems ; but also with theoretical evolutionary ecologists (ENS, ESE) to develop modeling of the evolution of pathogens facing practices promoting diversity.