oa Fungi-Induced Transformations of Dissolved Organic Matter in Soils: A Microcosm Incubation with 13C-Labelling

The current global change calls for a better understanding of the fate of organic matter (OM) in soils as it may act either as source or sink of atmospheric CO2. The present study thus aimed at studying the effect of fungal activity on different OM fractions of soils. Microcosm incubations were designed to monitor the elemental and molecular compositions of these fractions thanks to differential 13C-labelling of incubated litters (Italian Raygrass, Lolium multiflorum). Microcosms comprising vermiculite and 13C-litter were thus inoculated with Trichoderma harzianum, a common soil fungi, and characterized by a combination of analytical tools (enzyme assay, EA-IRMS, FTIR-ATR and Py-GC-MS) throughout a 6-month incubation. The present poster focuses on dissolved OM (DOM) that is often considered as the most reactive organic carbon pool in soils. This 6-month monitoring of litter-vermiculite microcosms first allowed highlighting the role of abiotic processes on DOC production. The fungus T. harzianum was mainly active during the first weeks of incubation, mineralizing not only abiotically released but also initial DOC, preferentially consuming carbohydrates. Fungal-induced modification of DOC also implied selective preservation of lipids and oxidation of lignin moieties.