Role of fungal denitrification in N2O fluxes from soils

土壤在缺氧条件下反硝化过程中产生温室气体N2O（氧化亚氮）。完全反硝化是指在细菌和真菌的催化下，通过亚硝酸盐、一氧化氮和N2O将硝酸盐依次还原为二氮（N2）。虽然许多细菌能够将N2O还原为N2，但大多数真菌却不能。因此，真菌通过土壤的反硝化作用对N2O排放的重大贡献是可以预期的。然而，真菌对反硝化的贡献相对于细菌的贡献尚未得到充分的研究，迄今为止还缺乏区分细菌和真菌N2O通量的精确方法。事实上，除了反硝化作用外，土壤中还可能同时发生其他几种N2O形成过程，这使得开发合适的方法变得复杂。因此，在项目的第一阶段，我们开发并评估了稳定同位素（“同位素体端元混合”，IEM）和微生物（通过qPCR表达真菌反硝化菌基因）方法来鉴定和量化真菌N2O产量。在项目的第二阶段，我们将继续开发新的方法，并将新开发的方法与现有的方法结合起来，研究真菌反硝化的调控，作为预测这一过程的基础，为制定减少土壤N2O通量的措施提供依据。我们的具体目标是：1。评估和改进量化和/或确定真菌对土壤源性N2O通量贡献的方法2。用改进的方法量化真菌对土壤源性N2O通量的贡献3。揭示真菌反硝化的控制及其与其他N2O和N2途径的相互作用4。确定真菌的关键角色及其调控。开发和测试生物地球化学模型的真菌反硝化算法。该工作计划将由位于布伦瑞克的th<s:1>新研究所和汉诺威莱布尼茨大学（LUH）的两个团队共同完成。th<s:1> nen工作计划将评估和改进抑制剂和稳定同位素方法，以量化真菌反硝化作用，并在有利于真菌或细菌反硝化的条件下在受控土壤培养中使用这些方法。LUH工作计划将扩展基于定量PCR的基因表达，仅针对窄范围的单个标记基因，以定量转录组学解决广泛的标记基因，从而开发有效的方法来研究真菌反硝化菌基因表达（FDGE）。稳定同位素和FDGE方法将联合用于进一步的土壤培养实验，以研究真菌反硝化的调节及其对土壤N2O通量的重要性。结果将有助于得出控制因素，将用于模拟真菌反硝化。

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.