Simulating decomposition of 14C‐labelled fresh organic matter in bulk soil and soil particle fractions at various temperatures and moisture contents |
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| Authors: | J‐M Séquaris M Herbst L Weihermüller J Bauer H Vereecken |
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| Institution: | 1. Agrosphere, ICG 4, Forschungszentrum Jülich GmbH, D‐52425 Jülich, Germany;2. Present address: LOEWE Biodiversity and Climate Research Centre, Frankfurt am Main, Frankfurt, Germany. |
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| Abstract: | 14C‐labelled fresh organic matter (FOM) was homogeneously incorporated into an agricultural topsoil of small total organic carbon (TOC) content in order to perform decomposition batch experiments at temperatures (T) ranging from 5 to 45°C and soil gravimetric water contents (w) ranging from 7 to 35%. After 4–6‐month incubation (tend), the residual 14C (Dend) was measured in bulk soil (0–2000 µm) and soil particle size fractions of 0–53, 53–200 and 200–2000 µm by chemical dispersion and sieving. The 14C‐FOM decomposition kinetics from soil were fitted either by a single first‐order reaction (rate constant, k0–2000) assuming only a one‐pool model in the bulk soil or by consecutive first‐order reactions (rate constants, k0–53 and k53–2000) assuming a two‐pool model in the bulk soil aggregate structure. In the latter case, a two‐step reaction mechanism involving a FOM particle‐size decrease along the soil fractions was considered where k0–53 was assumed to be a limiting rate constant. The 14C‐FOM decomposition kinetics was described for the experimental temperature and water ranges by Arrhenius and Michaelis‐Menten relationships, respectively. Additionally, the results obtained by the adapted Arrhenius physicochemical relationship were compared with the function proposed by Kirschbaum (1995) . Scaling functions Tm and wm were established and can be used to simulate FOM decomposition rates under different temperature and moisture level conditions. Modelling based on consecutive first‐order reactions supported the hypothesis that the circulation (inflow and outflow) of C into the soil particle small‐size fractions (<53 µm) controls the total C mineralization. |
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