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RESEARCH PRODUCT

Modelling denitrification including the dynamics of denitrifiers and their progressive ability to reduce nitrous oxide: comparison with batch experiments

subject

description

Nitrous oxide contributes to the global greenhouse effect and affects the chemistry of O 3 in the upper troposphere and lower stratosphere. To define a relevant model for microbial NO 3 - and N 2 O reductions in soil and estimate the parameters involved, we propose a method combining measurements of anaerobic soil slurry and simulations of NO 3 - and N 2 O reductions, including non-enzymatic competition between NO 3 - and N 2 O as electron acceptors and the microbial dynamics of two denitrifier groups that are either able or unable to reduce N 2 O. Three models varying in the description of soil capability to reduce N 2 O through denitrification were assessed. The procedure was applied on an arable soil known for its small N 2 O emissions in situ during wet events. Experiments consisted of N 2 O measurements in anoxic conditions (i) with C 2 H 2 , (ii) without C 2 H 2 or (iii) without C 2 H 2 and N 2 O addition, at various NO 3 - concentrations. The first model that accounts for microbial growth and considers a constant specific N 2 O reductase activity could not reproduce experimental data. It was necessary to consider that some denitrifiers initially unable to reduce N 2 O into N 2 became able to undertake this process. We evaluated two models taking into account the induction of N 2 O reductase, either with the progressive synthesis of this reductase simultaneously for all N 2 O reducers or with the sudden synthesis of this reductase distributed over a range of times for N 2 O reducers. Both models could approximately describe experimental kinetics, although some biases remained. The biomass of denitrifiers estimated by fitting simulated to experimental data was consistent with the biomass measured using chloroform fumigation-extraction and microbial enumeration.