Background and Objective

The greenhouse gas N₂O is formed by various microbiological processes in soils, where nitrification and denitrification play the major role. The contribution to N₂O formation of each microbial community is not sufficiently explored yet. Denitrification is conducted by both bacteria and fungi, but currently, N₂O formation by fungal denitrification is probably underestimated. A better understanding of sources of N₂O is essential for developing mitigation measures to reduce N₂O emissions.

The project is a collaboration between the University of Göttingen - Institute of Grassland Science, the Thünen Institute for Climate Smart Agriculture and the Technion - Israel Institute of Technology, Haifa. It aims at developing a new integrative method, based on FTIR spectroscopy for continuous monitoring of isotopic nitrogen species in soils as a tool to investigate short-term isotope and isotopologue dynamics and N₂O formation.

The aim of our project part is to quantify the contribution of fungi and bacteria on N₂O formation in soils as well as the associated isotope effects. We conduct incubation experiments to gain information on N₂O formation from denitrification and to show simultaneously the fungal and bacterial contributions to N₂O formation. Isotope effects of the source processes of N₂O emissions will be determined to check, how isotopic signatures can be used to identify these processes.

Target Group

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

Approach

Laboratory experiments are conducted with pure cultures and soils:

Incubation experiments with six soil fungi were used to characterize N₂O produced during fungal denitrification, with special emphasis on ¹⁵N site preference (SP) of N₂O to check how SP of N₂O is different from bacterial denitrification. The existence of oxygen exchange between water and denitrification intermediates during fungal denitrification was checked in a tracer experiment using ¹⁸O-enriched water.

 Incubation experiments were conducted with arable and grassland soils to distinguish between N₂O produced during bacterial and fungal denitrification using microbial growth inhibitors.

Our Research Questions

Pure culture experiments:

Is N₂O from six fungi characterized by higher SP-values compared to N₂O from bacteria?

Do fungi have an oxygen exchange between water and dentrification intermediates?

Soil incubation:

Do microbial growth inhibitors serve to differentiate between N₂O produced during denitrification by bacteria and fungi?

Do fungi existing in a soil community produce N₂O isotope values comparable to values known from pure fungal cultures?

Results

Rohe, L., Anderson, T.-H., Braker, G., Flessa, H., Giesemann, A., Wrage-Mönnig, N. and Well, R. (2014). Fungal oxygen exchange between denitrification intermediates and water. Rapid Commun. Mass Spectrom., 28: 377–384. doi:10.1002/rcm.6790

Rohe, L., Anderson, T.-H., Braker, G., Flessa, H., Giesemann, A., Lewicka-Szczebak, D., Wrage-Mönnig, N. and Well, R. (2014).Dual isotope and isotopomer signatures of nitrous oxide from fungal denitrification – a pure culture study. Rapid Commun. Mass Spectrom., 28, 1893–1903. doiI: 10.1002/rcm.6975