Dr Nicolas FANIN2, M Gonzague ALAVOINE3, Dr Isabelle BERTRAND1
1INRA UMR Eco&Sols, Montpellier, France, 2INRA UMR ISPA, Bordeaux, France, 3INRA UMR FARE, Reims, France
Soil C priming effect (PE) describes the change in the rate of soil organic matter (SOM) mineralization due to the addition of fresh organic matter (FOM), and is thus central to our evaluation of carbon (C) fluxes in terrestrial ecosystems. Towards a more mechanistic understanding of the terrestrial C cycle, our main objective was to evaluate dynamically the regulatory mechanisms that control PE. To do so, we followed the kinetics of C fluxes over 202 days and 23 dates after additions of two 13C-labeled plant litters varying in their initial quality from nutrient-rich and relatively accessible litter (non-mature wheat) to nutrient-poor and recalcitrant litter (flax stem) using four soil types originating from a land-use gradient (forest, plantation, grassland and cropland). We analyzed at three time points (at 27, 97, and 202 days) the mass loss rates for the main sugars within the cell wall, nutrient mineralization, hydrolytic and oxidative enzymes and the fate of the labeled 13C litters within the microbial biomass, the atmosphere and the SOM. We addressed for the first time the temporal dynamic in the main factors controlling PE by employing an a priori structural equation modelling (SEM) that allowed us to simultaneously test the effects of litter, soil and microbial parameters during FOM and SOM decomposition. Our results showed that FOM additions can rapidly stimulate a PE at the day-scale, with N availability playing a primordial role in the balance between FOM and SOM mineralization at the month-scale. However, C incorporation in the soil can counterbalance C losses via PE. Considering the temporal dynamic in the main drivers influencing PE can increase the predictive power of decomposition models that are currently limited by a lack of understanding in the regulatory mechanisms that control soil C fluxes from short- to long-term.
Biography: Isabelle BERTRAND is a senior scientist working on soil organic matter dynamic, its interactions with soil microorganisms and fauna. She is working on simple and complex agrosystems such as monocrops and agroforestry systems. Her focussed is in soil functional ecology and the soil C, N and P cycling.