Role of fungal denitrification in N2O fluxes from soils

• Applicants: Professor Dr. Marcus A. Horn; Privatdozent Dr. Reinhard Well
• Subject Area: Soil Sciences
• Term: since 2014
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 251282570

The greenhouse gas N2O (nitrous oxide) is produced during denitrification under anoxic conditions in soil. Complete denitrification is the sequential reduction of nitrate via nitrite, nitric oxide and N2O to dinitrogen (N2) and catalyzed by Bacteria as well as fungi. While many bacteria are capable of reducing N2O to N2, most fungi are not. Thus, a substantial contribution of fungi to N2O emission via denitrification from soil is to be anticipated. However, the contribution of fungi to denitrification relative to that of bacteria is not yet sufficiently investigated and precise methods to differentiate between N2O fluxes from bacteria and fungi are lacking to date. Indeed, the development of suitable methods is complicated by the fact that besides denitrification several other N2O forming processes can occur simultaneously in soil. Thus, we developed and evaluated stable isotope (“isotopomer endmember mixing”, IEM) and microbiological (fungal denitrifier gene expression by qPCR) methods to identify and quantify fungal N2O production during the first phase of our project. In the proposed second phase of the project, we will continue method development and use the new developed along with established methods to study the regulation of fungal denitrification as a basis to predict this process to provide a basis for developing measures to mitigate soil N2O fluxes. Our specific objectives are to:1. Evaluate and improve methods to quantify and/or identify the contribution of fungi to soil-derived N2O fluxes2. Quantify the contribution of fungi to soil-derived N2O fluxes with improved methods3. Unravel the control of fungal denitrification and interaction with other N2O and N2 pathways4. Identify fungal key players and their regulation5.Develop and test algorithms of fungal denitrification for biogeochemical models.The work program will be jointly accomplished by two teams hosted at the Thünen Institute in Braunschweig and the Leibniz University Hannover (LUH). The Thünen work program will evaluate and improve inhibitor and stable isotope approaches to quantify fungal denitrification and use those in controlled soil incubations under conditions favouring fungal or bacterial denitrification. The LUH work program will extend quantitative PCR based gene expression targeting only a narrow range of single marker genes to quantitative transcriptomics addressing a broad range of marker genes and thus to develop efficient methods to investigate fungal denitrifier gene expression (FDGE). Stable isotope and FDGE approaches will be jointly used in further soil incubation experiments to study regulation of fungal denitrification and its importance for N2O fluxes in soil. Results will serve to derive control factors that will be used to model fungal denitrification.

• DFG Programme: Research Grants