Nanoscale investigation of element and carbon transfer at the soil root interphase

Cornelia Rumpel^a, T. Lenhart^b, P. Poblete^ac , A. Vidal^b and M.L. Mora^c

^a CNRS/Institut of Ecology and Environmental Sciences, Paris, France

^bTechnical University Munich/Institute of Soil Science, Munich, Germany

^c BIOREN/Universidad de la Frontera, Temuco, Chile

cornelia.rumpel@inra.fr

Composting and vermicomposting are sustainable methods to transform organic waste materials into organic amendments providing plant nutrients and organic carbon to soils. The carbon sequestration of both materials may be improved by the addition of minerals and worms. The composition of the resulting organic amendments may affect plant growth nutrient uptake and carbon flow at the soil-root interphase. The study of these small scale processes benefits from new analytical developments. In the present study, we investigated (1) the effect of different types of compost (with and without addition of clay mineral and worms) on root and shoot biomass production of two contrasted plants (Fabaceae and Poaceae) and (2) the transfer of plant-derived carbon into different soil compartments.

Our conceptual approach consisted of using continuous stable isotope labeling and NanoSIMS analyses of the rhizospheric soil under two plant species grown for six weeks in microcosms filled with soil amended with contrasting organic amendments. Our results showed contrasting biomass production depending on the type of amendment. Two samples presenting contrasting elemental and isotopic results were selected for nano-scale secondary ion mass spectrometry (nanoSIMS) analyses in order to depict organo-mineral interactions and the incorporation of ¹³C at the root-soil interface. The rhizosphere represented a hotspot for plant-derived carbon compared to bulk soil, as reflected by the higher δ¹³C values in this compartment, especially with composts and vermicomposts produced in the presence of clay minerals. Nanoscale analyses allowed to identify contrasting microbial functioning, which is strongly impacting carbon and element transfer from plants to soil.