P2 Regulation, ecophysiology, and kinetic parameters of uncultured N-gas flux associated anaerobic microbial communities in agricultural soils [funded by DFG]

Project staff:

M.Sc. Sina Henjes
Prof. Marcus A. Horn


Denitrifiers (reducing N-oxides to N2O and/ or N2), non-denitrifying N2O-reducers (reduce N2O to N2), and dissimilatory nitrate reducers (DNRA; reduce N-oxides to NH4+) are facultative or obligate anaerobes that impact the emission of the greenhouse gas N2O as well as retention of nitrogen. Non-denitrifying N2O-reducers and DNRA compete with denitrifiers for electron donors. Distinct microbial taxa have distinct ecophysiological traits determining their competitiveness and N-gas production capabilities, and will consequently respond differently to environmental conditions. However, such traits are essentially unknown for uncultured taxa despite their importance for N-gas emissions and N-retention in soils. Thus, the following hypotheses will be addressed: (i) Denitrification response to environmental factors is shaped by contrasting microbial communities including hitherto unknown species, and can be explained by their intrinsic ecophysiological properties. (ii) Gene expression and community structure associated with denitrification, N2O-reduction and DNRA reflect metabolic states and potentials, thus increasing predictability of N2O and N2 fluxes. High-throughput incubations under various conditions (including 15N-tracers) combined with functional gene expression, as well as gene and transcript based next generation sequencing will be applied to identify apparent Michaelis-Menten and physiological parameters. Functional genes of denitrifiers (nirK/S encoding nitrite reductases yielding NO; nosZI encoding N2O reductase yielding N2), non-denitrifying N2O reducers (nosZII encoding N2O reductases yielding N2), and DNRA (nrfA encoding nitrite reductases yielding NH4+), will be primarily analysed. Response patterns of target communities and/or functional gene expression to defined environmental paramters will be obtained in microcosms. The effect of environmental control factors of N-gas fluxes and plant roots on target communities will be identified in mesocosms. Data will be integrated in the development of an extended denitrifier-regulatory-phenotype-concept and will give insights into the ecophysiology and competition of denitrifiers, non-denitrifying N2O-reducers, and DNRA under various conditions. Response functions of such groups towards organic carbon (i.e., electron donors), nitrate, and nitrous oxide, their growth rates, maintenance rates and community structure will be provided for modelling of denitrification and N-gas fluxes.