Control of fungal denitrification in soils

Background and Objective

Microorganisms are capable of performing denitrification under anoxic soil conditions; meaning reducing nitrate or nitrite and thus the greenhouse gas nitrous oxide (N₂O) and dinitrogen (N₂) can be released. Even after decades of research, it has not yet been conclusively clarified how much fungi contribute to the production of N₂O during denitrification in soil.

The latest studies have shown that probably only a few species are capable of denitrifying (Keuschnig et al. 2020). However, the contribution to the total emissions from denitrification could be high, because fungi, unlike bacteria, cannot reduce N₂O any further to N₂.

Because many N₂O producing processes (e.g. denitrification, nitrification and codenitrification) can co-occur in soil, it is difficult to clearly determine the contribution of fungi to denitrification by N₂O release from soils. Nevertheless, in order to improve modelling of N₂O emissions or to develop mitigation strategies, a more precise understanding of the process is necessary.

This follow-up project aims to combine different experimental approaches and thus to develop a method that can be used to quantify N₂O emissions from fungal denitrification.

Target Group

Science, Federal Ministry of Food and Agriculture, associations of agriculture and environmental protection

Approach

Based on previous studies, substrate-induced respiration with selective inhibition (SIRIN) and the analysis of stable isotopes in nitrous oxide will be used to determine the proportion of N₂O produced by fungi in controlled incubation experiments. However, validation of these methods has not yet been carried out.

Therefore, it is planned to improve these methods and test for correctness of results in controlled laboratory incubation experiments. This includes checking and testing inhibitors used for bacteria and fungi and whether the isotope signatures in N₂O resulting from pure cultures are comparable with those of the soil community. Part of these controlled incubations are incubations of extracted communities in sterile medium, but also in sterile soil. In addition, different soils with varying conditions (e.g. oxygen availability, temperature, carbon source, electron acceptor) will be incubated. The isotopic signatures will be measured and methods using the polymerase chain reaction (PCR) will be used to analyze fungal communities that contribute to denitrification or even the gene expression of the fungal NO reductase (P450nor). Results of fungal denitrification could potentially be included in models calculating N₂O emissions.

Our Research Questions

Do the isotopic signatures of N₂O from denitrifying microorganisms depend solely on the enzymes but not on soil conditions?

Can isotopic signatures of N₂O and associated isotope effects be used to estimate the contribution of fungal denitrification to N₂O emissions from soils?

Do differences exist between controlling factors of fungal and bacterial denitrification?