Elucidating the importance of the pools of nitrate in soils on denitrification

本研究的目的是确定的因素控制硝化和反硝化，即现有的NO3-，新形成的NO3-和添加的NO3-的不同池的N的利用。不同池的NO3-在土壤中的存在已建议通过一系列的实验室培养实验，使用反硝化培养系统，DENIS，在北怀克的Rothamsted研究。这是从排放的N2 O的同位素特征数据中观察到的。据预计，在土壤核心的N和C的应用程序后，在delta 15 Nbulk-N2 O的增加将导致由于微生物的偏好，使用较轻的同位素，留下一个富集池。这种增加发生在施用N和C后的几天，但随后观察到减少。这种行为的变化结合使用的模型表明，可能的变化之间的NO3-添加NO3-和原生土壤池的NO3源。第三个NO3-池，来自所施加的NH 4+的硝化作用，也可以通过反硝化作用和硝化作用成为N2 O的来源。硝化和反硝化可能同时发生在土壤中，但往往有不确定性，其中过程占主导地位，在特定的土壤在特定的条件下，为了制定减缓N2 O排放的策略，这是必要的，以获得知识的来源和过程中产生的N2 O在土壤中，并了解这些过程的控制因素，以具体针对这些来源。本研究旨在确定控制硝化/反硝化中不同NO3-库利用的因素，即i）现有NO3-，ii）新形成的NO3-和iii）添加的NO3-。土壤水分（充满水的孔隙空间）和施用C：N的比例将是研究的控制因素，为了实现总体目标，将通过使用实验室培养系统（DENIS）进行施用N和C后的释放气体N2 O、N2、NO、N2 O的同位素异构体的直接测量。当应用标记的N源时，也将测量15 N-N2 O。N2 O的同位素异构体描述了天然丰度下N2 O分子上15 N的位置，并可用于确认工艺来源。这些数据将被用于一个模型中，以评估现有的（土壤NO3-）和添加NO3-的反硝化利用的土壤在两个不同的C：N的比例在添加的amendment.Isotope标记技术将被应用结合一个模型（Müller模型），能够确定同步复杂的转换率的N，允许量化的硝化反应速率，矿化，固定化和再矿化在新形成的微生物生物量。该技术将提供来自硝化的NH 4+和添加的NO3-的N2 O来源的估计。（大孔和微孔）孔隙-心模型将用于预测10至100微米尺度的生物活性热点的位置，与营养物质（N和C）运输的临界渗滤路径有关。通过直接气体测量（NO、N2 O和N2）和同位素技术的组合，通过标记和使用稳定同位素，将有可能区分脱氮过程中涉及的不同NO3-池。该项目将从三个数学模型中获得模型改进和见解;最后将为土壤管理提供建议，以减少N2 O排放。

The aim of this study is to determine the factors controlling the utilisation of different pools of N in nitrification and denitrification, namely existing NO3-, newly formed NO3- and added NO3-.The existence of different pools of NO3- in soils has been suggested through a series of laboratory incubation experiments using a denitrification incubation system, DENIS, at Rothamsted Research, North Wyke. This was observed from data on the isotopic signature of the emitted N2O. It was expected that after application of N and C to soil cores, an increase in the delta15Nbulk-N2O would result due to the preference of the microbes to use the lighter isotope, leaving an enriched pool behind. This increase occurred for several days after N and C application but then a decrease was observed. This change in behavior combined with the use of a model suggested the possible change in the source of NO3- between the added NO3- and the native soil pool. A third NO3- pool, from the nitrification of applied NH4+, can also be a source of N2O via denitrification and also from nitrification. Nitrification and denitrification may occur simultaneously in soil but there is often uncertainty associated with which process dominates in a particular soil under specific conditions.In order to develop mitigation strategies for N2O emissions, it is necessary to gain knowledge of the sources and processes that produce N2O in soils, and to understand the controlling factors of these processes to specifically target these sources. This study aims to determine the factors controlling the utilization of different NO3- pools in nitrification/denitrification, namely i) existing NO3-, ii) newly formed NO3- and iii) added NO3-. Soil moisture (water filled pore space) and the ratios of applied C:N will be the controlling factors studied and in order to achieve the overall aim, direct measurements of evolved gases N2O, N2, NO, isotopomers of N2O after application of N and C will be carried out by using the laboratory incubation system (DENIS). Also 15N-N2O will be measured when applying a labeled N source. Isotopomers of N2O describe the location of the 15N on the N2O molecule at natural abundance and are useful for confirmation of the process source. This data will be used in a model to assess the utilization for denitrification of both existing (soil NO3-) and added NO3- to soil at two different ratios of C:N in the added amendment.Isotope labelling techniques will be applied combined with a model (Müller model) capable of determining rates of simultaneous complex transformations of N, allowing the quantification of reaction rates of nitrification, mineralisation, immobilisation and re-mineralisation in newly formed microbial biomass. This technique will provide an estimate of the source of N2O from nitrified NH4+ and NO3- added.A further model - the dual porous (macro and micropores) Pore-Cor model will be used to predict the location of hot spots of biological activity at the 10 to 100 um scale in relation to the critical percolation path where the transport of nutrients (N and C) occurs.Through a combination of direct gaseous measurements (NO, N2O and N2) and isotopic techniques, via labelling and use of stable isotopes, it will be possible to differentiate between the different pools of NO3- involved in the process of denitrification. The project will achieve model refinements and insights gained from three mathematical models; and finally will provide recommendations for soil management to reduce N2O emissions.