Vegetated subsoil exposed during geotechnical operations has massive carbon storage potential: a study of 13C partitioning into soil respiration and different soil fractions

Mr Lorenzo Rossi1,7, Dr. Alexia Stokes1, Dr. Rémi Cardinael2, Dr. Luis Merino-Martin1,9, Dr. Delphine Derrien3, Dr. Alex Milcu4,5, Dr. Jaques Roy4, Mr. Sébastien  Devidal4, Dr. Clément Piel4, Dr. Caroline Plain6, Prof. Giacomo  Russo7,8, Dr. Zhun Mao1

1AMAP, Inra, Ird, Cirad, Cnrs, University of Montpellier, Montpellier Cedex 5, France, 2UPR Aida – CIRAD,  Montpellier, France, 3INRA, Biogéochimie des Ecosystèmes Forestiers, UR1138, Champenoux, France, 4Ecotron Européen de Montpellier, Unité Propre de Service 3248, CNRS, Campus Baillarguet, F-34980 , Montferrier-sur-Lez, France, 5CNRS, CEFE – Unité Mixte de Recherche 5175, Université de Montpellier, Université Paul Valéry, École Pratique des Hautes Études, Montpellier Cedex 5, France, 6Université de Lorraine, AgroParisTech, INRA, UMR Silva, F-54000, Nancy, France, 7University of Cassino, Via Di Biasio 43, 03043  , Cassino, Italy, 8University of Naples Federico II, Department of Earth Science Environment and Resources, Naples, Italy, 9CEFE, CNRS, Univ Montpellier, Univ Paul Valéry Montpellier 3, EPHE, IRD, , Montpellier, France

Geotechnical operations such as embankment construction influence soil carbon (C) storage since massive amounts of C-poor subsoil are brought to the surface. We hypothesize that subsoil can sequester relatively more C than C-rich topsoil due to its lower C-saturation. We excavated topsoil (0.0 to 0.3 m) and subsoil (1.1 to 1.4 m) from the same profile. We sieved soil and sowed Medicago sativa and Lolium perenne (n=6 pots of each species x soil). Controls were soil with no vegetation (n=6 x soil). To trace the fate of C, pots were incubated for 6 months under a continuously 13C-enriched-CO2 (2%) in three growth chambers with controlled conditions. Soil respiration (CO2 and 13C) was quantified every 2 weeks and was higher in the topsoil, due to greater root and microbiological activity. The 13C enrichment of the respired C was significantly higher in M. sativa regardless of soil type. After 6 months, soils were divided into four different fractions: particulate organic matter (POM), fine POM, silt, silt+clay, and total C and 13C enrichment were analyzed. Results show that the total C (g new C/cm3 soil) stored depended on root biomass. Topsoil had significantly more biomass, and stored more labeled plant derived-C, especially under M. sativa. However, when results were weighted as new C stored in cm3 of soil per g of root biomass, subsoil stored relatively more C, especially in POM and silt+clay fractions (increase in new C stored in subsoil compared to topsoil for POM: M. sativa +135%, L. perenne +33% and for silt+clay: M. sativa +56%, L. perenne +16%). The higher relative increase of organo-mineral protected C in subsoil corroborates the hypothesis that C saturation influences C storage and protection. Vegetating subsoil with appropriate species could act as a major C sink, valorizing geotechnical infrastructures as resources for carbon storage.


Biography: Lorenzo Rossi is an agronomist specialized in soil sciences, currently carrying out his Joint Ph.D. between INRA Montpellier and Cassino University. His study focuses on sustainable geotechnical infrastructures and technologies, more specifically he is investigating the potential of embankments to act as active carbon sinks

SOIL ORGANIC MATTER

7th International Symposium
Soil Organic Matter

6 – 11 October 2019

Hilton Adelaide

Adelaide, South Australia

Australia

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