Species and root traits control C stabilization in the rhizospheric soil of a Mediterranean common garden experiment

Prof. Vincent Poirier1, Dr. Catherine Roumet2, Dr. Grégoire Freschet3, Prof. Alison Munson4

1University of Québec in Abitibi-Témiscamingue (UQAT), Notre-Dame-du-Nord, Canada; 2Centre National de la Recherche Scientifique (CNRS), Montpellier, France; 3Centre National de la Recherche Scientifique (CNRS), Moulis, France; 4Laval University, Québec, Canada

The objective of this work was to evaluate how the roots of different plant species and life forms affected soil organic carbon (SOC) stabilization. We analyzed the soil attached to the roots (i.e., rhizospheric soil) under 13 Mediterranean species grown in monocultures in a common garden experiment for four years, and compared it to a bare soil kept free of vegetation. We used a density fractionation procedure to separate uncomplexed organic matter found in the light fraction of the rhizospheric soil from mineral-associated organic matter found in the dense fraction. We measured root traits and SOC concentration in the rhizospheric bulk soil and its fractions. We used a comparative approach to test significant differences among species, and explored relationships between root traits and SOC stabilization. We observed that the concentration of mineral-associated SOC in rhizospheric soil was on average 40% greater than that in the bare soil, with a strong effect of plant species (P < 0.0001). Some species such as Bromus erectus, Centaurea pectinata and Festuca christianii-bernardii showed increases up to 60%. Root morphology and architecture exert strong control over SOC stabilization in the rhizospheric soil. Increased specific root length (SRL), root length density (RLD) and the proportion of very fine (<0.2 mm) roots promoted greater mineral-associated SOC in the rhizosphere, while increased root diameter and proportion of coarse (1-2 mm) roots had the opposite effect. Overall, our results suggest that plant species with morphological and architectural root traits related to resource acquisition (i.e., fine roots with high SRL and high RLD) favor the stabilization of SOC in the rhizosphere more than species with root traits related to resource conservation (i.e, high proportion of thick roots).


Vincent Poirier is Professor and Scientific Director of the Agriculture and Agri-food Research and Development Unit of the University of Québec in Abitibi-Témiscamingue (UQAT). He holds two master’s degrees in soils and environment (2005, 2007) from Laval University and a doctorate in renewable resources (2011) from McGill University, Canada. Before starting as a professor at UQAT in 2017, he completed postdoctoral training at Laval University in collaboration with the Center for Functional and Evolutionary Ecology in Montpellier, France.

His team’s research focuses on 1) investigation of soil organic matter, carbon storage and the roles of roots in soil functioning in top- and subsoil horizons; 2) production, exploitation and conservation of fodder plants to support livestock farming; 3) management and production of conventional and organic field crops. His research team is currently involved in a dozen research projects mainly related to soils in temperate agroecosystems, and some focus on urban and forest soils as well as soils in tropical environments.


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