Context
Agroecosystems today are identified on both sides of the spectrum concerning climate change. They can be a source or sink of GreenHouse Gases (GHG) and therefore a key actor in mitigation. Those same ecosystems are also highly affected by climate change that impacts their production, exchanges of contaminants and GHGs, their efficiency in acquiring and using resources, as well as their exposition to new biotic threats. This, among other issues, leads farmers to adapt their management practices to insure sufficient efficiency and durability. Countries are increasing their focus on achieving net reductions of GHG emissions from agriculture as necessary conditions to meet the climate targets that the international community has set at the Paris Agreement on climate change of the UN Framework. This also includes possibilities for enhancing soil organic carbon (SOC) stocks but also mitigation through changes in surface albedo, for which a substantial part of the possibilities would occur through changes in cropping systems and land use. It is therefore essential to be able to quantify the full climate mitigation potential of agroecosystems associated to adaptations strategies while maintaining productivity and increasing efficiency for resource use. One of the challenges today is to better account for cropping systems in the conception and evaluation of the different mitigation and adaptations strategies. This implies having a better knowledge of plant functioning in a fluctuating environment and of biogeochemical processes within agroecosystems, with a special focus on soils and to appraise the interactions between processes and feedbacks whether negative or positive.
An investment in research is necessary on processes that govern (i) soil carbon (C) and nitrogen (N) dynamics and their coupling in soils, (ii) plant growth, functioning and exchanges with the soil and atmosphere in response to climatic conditions, including plant health aspects.
Scientific questions and objectives
In the coming years we will try to provide a better understanding of:
- How agroecosystems contribute to greenhouse gas emissions (CO2, N2O, CH4, O3), as well as aerosols and their precursors (NH3, VOC, NO, O3, HONO);
- How different adaptation strategies (agricultural practices, species selection) contribute to increasing SOC stocks and to reducing GHG emissions in relation to environmental conditions;
- How a better understanding of agroecosystem functioning including plant health can help us mitigate climate change.
In relation to these objectives, we will address the following scientific questions:
- What are the trade-offs between C sequestration, reduction of GHG emissions, water quality, air pollution and other ecosystem services?
- How do different abiotic (contaminants, water, temperature) and biotic stresses (epidemics and pests) affect GHG emissions, C sequestration, and emissions of different air contaminants?
- What are the benefits of carbon sequestration in soils for soil properties and ecosystem services?
- What is the effect of agroecological practices on GHG emissions and C sequestration?
- How will different crop residue management and recycling of organic biomasses impact soil functioning?
- How will plant microclimate impact crop health?
- Are we able to identify alternative ways to limit climate change impacts on crop production and health?
- How can we account for the complexity of biogeochemical processes taking place at the soil pore space scale
for incorporation into higher spatial scales such as the soil profile or plot?
- What are the regulations for the biodegradation of soil organic matter at a microscale level of spatial organization?
- Is it possible to improve the knowledge of denitrification determinism at the level of the soil structure, also taking into account accessibility of nutrients to the microorganisms according to specific soil pore connectivity’s and the relation to SOC?
- What is the role of the plant root system on C sequestration and GHG emissions?
- How do different plant organs contribute to carbon storage under different abiotic stresses?
- What is the role and the impact of rhizo-deposition (e.g. root exudation, root senescence)?
Insertion within ECOSYS
The different ECOSYS’teams contribute to this structuring theme both through modeling and experimental actions. We will build upon the different experimental expertise on SOC storage, soil biogeochemistry in relation to soil environmental conditions and management practices with field experiments as well as laboratory based experiments, and satellite or drone based measurements of SOC storage and GHG emissions. Several long-term experiments are managed and run by ECOSYS namely the SOERE-PRO platform, the Long Term Bare Fallow experiments, the “La Cage” long term experiment as well as the Grignon ICOS site (part of the European infrastructure dedicated observation and monitoring over the long term of GHG fluxes). The expertise and use of carbon isotopic biogeochemistry allows the identification of sources, the quantification of kinetics and the characterization of processes, especially about microbial processes and to the long-term stabilization of the organic matter. Different models were developed and are still implemented at different scales going form the microscale (LBIOS and MOSAIC), passing by the plot scale (CERES-EGC, STICS, Cantis, NCsoil, SoilV platform) and going to the regional and global scales (CERES-France, Farmsim), including the landscape scale (Nitroscape).
This structuring theme is linked to other structuring themes within ECOSYS. There is a tight interaction with the “Exposure to and effects of contaminants in agroecosystems” theme through the overlap with the study of contaminants exchanges (O3, NH3, VOC, aerosols). There is a link as well with the “Diversity from field to landscape for a resilient agroecosystem with limited impact” theme since the landscape scale is the key scale for implementing new management practices, accounting for interactions between climate change, plant-fungus and pest management, and seeking for resilient management. Lastly there is also a link to the “Managing, producing and recycling biomasses for multiple purposes” theme through the impact of different organic matter additions on SOC stocks and GHG emissions.
The action plan of this structuring theme will highly rely on promoting interactions between Eco&Phy and Soil teams especially concerning SOC stocks and modeling coupling and integration. Several newly started projects and PhDs as well projects under construction will contribute to tackle some of the scientific questions raised. We will rely on:
- The work of a newly recruited researcher focusing on how root systems contribute to SOC dynamics is structuring for this theme.
- Our participation in the FACCE-JPI RESIDUEGAS project as well as the PhD project part of RESIDUEGAS, which will contribute in increasing our understanding on gaseous Nitrogen Emissions from residue decomposition in soils.
- Our participation in the CLAND “Convergence Institute” and our implication in the “land based climate mitigation” challenge with two PhD projects co-supervised by ECOSYS and set to start in fall 2018 for one and fall 2019 for the second.
- Several newly started projects funded by ANR or ADEME (STORESOIL, SEMOIRS, PROTERR).
