RhizoSeqC

In the context of climate change and food security, the major challenge for intensive agrosystems is to switch field crop soils from a carbon (C) destocking status to a C storage status. Two levers can be used to achieve this reversal of C sequestration trajectories: increasing C inputs directly into the soil and encouraging the stabilisation of organic matter (OM) in the soil. The challenge is therefore to develop cropping systems capable of combining these levers while maintaining economically attractive production.

RhizoSeqC tackles C sequestration solutions by proposing to use a combination of plants of agricultural interest selected to increase C rhizodeposition and additions of stabilising mineral phases. The project is organised into 6 work packages, including a coordination work package (WP0). It explores the hypothesis that the continuum of plants (WP1), bacterial communities (WP2) and soil organo-mineral associations (WP3) can be optimised to increase soil carbon sequestration (WP5), while meeting agronomic requirements (WP4). The plant of agricultural interest selected is sorghum (grain cereal, fodder) for its importance in terms of food security and its ability to adapt to the effects of climate change (water stress and warming). The reference soil type chosen for cross-referencing the results of the work packages is arenosol, because of its low and fragile native OM content and its wide distribution in the North and South, although work package 4 will enable plants to be tested on other soil types. WP1 is focusing on sorghum rhizodeposition in order to identify the genome zones (QTLs) controlling soil OM inputs. Variety selection is based on optimising the formation of the soil mantle around the roots. In WP2, using stable isotope tracing and the omicsWe are focusing on the impacts of rhizodeposition on microbial communities and on the stoichiometry of C/N coupling in biotransformations, with particular emphasis on the priming-effect which could have a negative effect by reducing the C stock initially present. WP3 focuses on the fate of rhizodeposited C in different types of soil and its stabilisation by organo-mineral interactions. Isotopic marking approaches are also being used to draw up a C balance sheet (input/output/gain). as well as monitoring the fate of C using imaging techniques in situ. WP4 is evaluating the agronomic properties of sorghum lines selected on experimental sites with contrasting climates (France and Senegal). Work package 5 will capitalise on the results of the first four work packages by applying them in the field in order to quantify carbon sequestration accurately using isotopes and to predict it using modelling.

With its 11 partners, RhizoSeqC structures a multidisciplinary community of scientists and operational players on a national and international North/South scale. The research institutes involved are CNRS, IRD, CIRAD, INRAE and its Senegalese equivalent ISRA, CEA, ENS and 2 universities (Rouen and PSL). RhizoSeqC is mainly in line with the priorities of axis 3 of the PEPR on three fronts:(1) " increase soil C stocks ", (2) " better quantify the contribution and effectiveness of plant roots and rhizosphere in sequestering organic matter". and (3) "Searching for plant production solutions that anticipate future climatic conditions".

The results of RhizoSeqC are expected to promote agro-ecological innovations in cereal-growing systems in the North and South. These innovations will help to increase carbon sequestration in soils, thereby helping to meet C neutrality targets while taking future climate constraints into account.