Is it root- or soil-derived carbon that drives denitrification?

土壤微生物的反硝化过程产生一氧化二氮(N2O)和氮素(N2)，它们被排放到大气中。虽然氮气在大气中是无害的，但由于这种气体参与了全球变暖和平流层臭氧的破坏，N2O的排放令人担忧。由于土壤是N2O的重要来源，了解对其产生和还原为无害氮气的控制是至关重要的。一种这样的控制是碳(C)的有效性，但这是关于反硝化菌-N2O产生的最不为人所知的因素，而且用于反硝化的主要碳源尚不清楚。与土壤有机质(SOM)相比，来自活根的C被认为选择了更活跃、更丰富和更独特的微生物群落，因此假设导致反硝化菌-N2O和-N_2的产生数量和速率不同。然而，这种动态碳源在不同SOM-C背景下驱动反硝化的意义以及如何选择到氮气的完全反硝化是未知的，因此目前预测模型中忽略了这一点。该项目将确定植物来源的碳流在多大程度上推动不同土壤有机质含量的土壤中的反硝化作用，以及管理历史。我们将使用最先进的稳定同位素技术来量化反硝化过程中N2O和N2的产生，并将其与微生物群落对C的利用、根际反硝化细菌的活动以及参与N2O产生和还原的基因上调有关。所获得的信息将是制定通过SOM管理减少N2O排放的战略所必需的，并将被纳入目前忽略根C流贡献的预测模型中。

The soil microbial process of denitrification produces nitrous oxide (N2O) and dinitrogen (N2) which are emitted to the atmosphere. Whilst N2 is harmless in the atmosphere, emissions of N2O are of concern due to the involvement of this gas in global warming and the destruction of stratospheric ozone. Since soil is a significant source of N2O it is vital to understand the controls on both its production and its reduction to harmless N2. One such control is carbon (C) availability, but this is the least well understood factor with regards to denitrifier-N2O production and the predominant C source used in denitrification is unknown. C from living roots is thought to select for a more active, abundant and distinct microbial community compared to that associated with soil organic matter (SOM), and is therefore hypothesised to result in different quantities and rates of denitrifier-N2O and -N2 production. However, the significance of this dynamic C source in driving denitrification against different backgrounds of SOM-C, and how this selects for complete denitrification through to N2 is unknown, and so is currently ignored in predictive models. This project will determine the extent to which plant-derived C flow drives denitrification in soils of different SOM contents, and management histories. We will use state-of-the-art stable isotope techniques to quantify N2O and N2 production during denitrification and relate this to C utilisation by the microbial community, the activity of denitrifying bacteria in the rhizosphere and the up-regulation of genes involved in N2O production and reduction. Information obtained will be essential for the development of strategies to mitigate N2O emissions through SOM management, and will feed into predictive models which currently ignore the contribution of root-C flow.