PEPR FairCN RhizoSeqC

In the current climate change and food security setting, the major challenge for intensive agrosystems is to shift the status of cropland soils from a carbon (C) continuous depletion to a C sequestration trajectory. Two levers can be used to achieve this reversal in C storage trajectories: increase direct soil C inputs, and promote soil OM stabilization. The challenge is therefore to develop cropping systems capable of combining these levers while maintaining economically attractive production. RhizoSeqC tackles the C sequestration issue using a combination of selected plants to increase C rhizodeposition and inputs of stabilizing mineral phases. The project is organized in 6 work packages, including a coordination package (WP0). It explores the hypothesis that the plant (WP1), bacterial community (WP2), soil organomineral association (WP3) continuum can, while meeting agronomic requirements (WP4), be optimized to increase soil carbon sequestration (WP5). The selected plant species of agricultural interest is sorghum, which has been selected for its role in food security worldwide (over 300 million people in the semiarid tropics depend on sorghum on a daily basis) and drought stress adaptation properties. Arenosol is the reference soil type assessed throughout the WPs because of its low fragile native OM content and widespread distribution in the Global North and South, while keeping in mind that in a task plants can also be tested on other soil types. WP1 focuses on sorghum rhizodeposition to identify genome zones (QTLs) controlling soil OM inputs. Selection of the optimized varieties is based on rhizosheath formation. In WP2, we use stable isotope probing and omics approaches to assess the impact of rhizodeposition on microbial communities, while specifically focusing on the priming effect, which could have the drawback of decreasing the initial pristine soil C stock. WP3 focuses on the fate and stabilization of rhizodeposited C in different types of soils and its stabilization by organomineral interactions. Isotopic labeling approaches may also be used to quantify a budget (input/output/gain), as well as track the fate of C via in situ imaging techniques. WP4 evaluates the agronomic properties of selected sorghum lines at experimental sites with contrasting climates (France and Senegal). WP5 capitalizes on the results by applying them in the field to precisely quantify carbon sequestration by isotopy and predict it by modelling. With its 11 partners, RhizoSeqC structures—on a national and international North/South scale—a multidisciplinary community of scientists and operational actors committed to offering their expertise to benefit research oriented towards sustainable solutions in economically relevant crop production systems. The research institutes involved are CNRS, IRD, CIRAD, INRAE, INSA, CEA, ENS, Rouen University and PSL University. They are associated with a Senegalese national research institute (CERAAS/ISRA) and a research unit (UE APC). The requested aid amounts to k€1,250 for the overall 5 years project. RhizoSeqC is in line with the priorities of axis 3 of the FAIRCarboN PEPR in three areas, namely: (1) “increase soil C stocks” (2) “better quantify the contribution and efficiency of plant roots and rhizosphere in sequestering organic matter (OM)” and (3) “seek plant production solutions that anticipate future climatic conditions”. It is expected that joint approaches implemented in Global North and South cereal-based agrosystems will serve as mutual levers to achieve scientific and agronomic advances, while fostering structuring of the North/South international scientific community. With the innovation targeted by RhizoSeqC, we also expect changes in agroecological practices in favor of higher carbon sequestration in the C neutrality and future climate change framework.

Contribution LSCE : Using isotopic organic geochemistry (¹³C, ¹⁴C), the LSCE evaluates the long-term sustanability of the proposed solutions.