Uncharacterised microbial pathways are key to understanding large fluxes of biogenic reactive nitrogen gases from agronomic soils

大气反应性氮氧化物气体(NOY=NO+NO2+HONO+...)通过人为活动(主要是燃烧)、土壤氮和土壤微生物活动之间复杂的相互作用网络，与地球的氮循环相耦合。土壤氮素排放的生物地球化学传统上被认为是由氮气(N2)和一氧化二氮(N2O)主导的；然而，卫星、模拟和实验室研究表明，土壤中NOY的排放量可能比这些更常见的氮气更大。NOY在大气化学中是重要的臭氧前体，在酸雨的形成中起着关键作用。NOY也被认为是二次空气污染物--已知会加重哮喘和支气管炎，特别是在青少年和老年人口中。除了人为来源外，自然非点源产生的NOO气体包括土壤(占NOO排放总量的24%)、野火(19%)和闪电(13%)。然而，人们对这些自然来源的NOx通量知之甚少，尽管它们占所有大气NOx的50%-随着机动车和工业排放的持续下降，这一比例正在增加。重要的是，关于生物(微生物衍生)产生机制的信息严重缺乏，导致不准确的NOY耦合气候模型预测。这主要可以归因于对二氧化氮(NO2)和亚硝酸(HONO)等主要NO物种的形成缺乏了解。我们怀疑存在尚未发现的产生NOY的途径，这些途径是由来自所有三个生命领域的大量微生物催化的。我们假设的机制来自人类生理学，在人类生理学中，NOY物种被认为是重要的信号分子。我们将在农艺土壤中探索这些机制，因为土壤是NO气体的最大自然来源，并且在我们的初步工作表明，这些土壤产生的NON明显多于其他陆地系统，如草原和林地。我们将通过对英国一种主要的商业作物(小麦)的田间试验来进一步定义农艺-黑色，包括四个具有不同地上和地下特征的品种。确定这些不同品种的NOY土壤排放将是至关重要的，因为不同的植物性状，如特定的根长，可以影响土壤N循环微生物群-这将不可避免地影响NOY排放。还将探讨其他重要变量，包括化肥施用量和NOY通量的空间变异性。重要的是，我们还将尝试确定土壤铁和铁形态对N循环群落组成和NOY通量的作用。土壤铁是我们理论NOY机制的一个重要方面--刺激活性氧的产生，而活性氧是NOY产生的关键反应物。我们将从英格兰各地的不同农场寻找含铁量不同的土壤，用于小麦中微体研究。将测量土壤NOY通量，并将其与矿物学特征和N循环群落大小联系起来。总体而言，该项目将确定关于主要氮氧化物生物产生机制的基本知识，提供对一种主要全球作物的土壤氮素通量的直接测量，并有助于更好地了解土壤中碳-养分-矿物的耦合循环。此外，这项工作代表着对土壤氮素动力学认识的重大变化，将是第一批将鸟枪元基因组学和依赖于培养的方法与大气化学过程相结合的方法之一，并将代表着大气NOY计算的重大进展。

Atmospheric reactive nitrogen oxide gases (NOy = NO + NO2 + HONO + ...) are coupled to Earth's nitrogen cycle through an intricate network of interactions between anthropogenic activity (primarily combustion), soil nitrogen, and soil microbial activity. The biogeochemistry of soil nitrogen emissions is traditionally thought to be dominated by nitrogen gas (N2) and nitrous oxide (N2O); however, satellite, modelling, and laboratory studies show NOy emissions from soil can be of greater magnitude than these more commonly measured nitrogen gases. NOy are important in atmospheric chemistry as precursors to ozone (O3) and play a key role in the formation of acid rain. NOy are also considered secondary air pollutants - known to worsen asthma and bronchitis, especially in adolescent and geriatric populations. In addition to anthropogenic sources, NOy gases are produced from natural non-point sources including soil (24% of total NOy emissions), wildfires (19%), and lightning (13%). However, very little is known about NOy fluxes from these natural sources even though they account for 50% of all atmospheric NOy - with this percentage increasing as vehicle and industry emissions continue to decline. Importantly, there is a critical lack of information regarding biogenic (microbiologically derived) production mechanisms, resulting in inaccurate NOy-coupled climate model projections. This can be primarily attributed to a lack of understanding regarding the formation of major NOy species, such as nitrogen dioxide (NO2) and nitrous acid (HONO). We suspect there are yet undiscovered NOy-producing pathways, catalysed by a vast array of microbes from all three domains of life. Our hypothesised mechanisms are derived from human physiology, where NOy species are known to be important signalling molecules. We will explore these mechanisms in agronomic soils, as soils are the largest natural source of NOy gases, and within an agronomic context as our preliminary work has shown that these soils produce significantly more NOy than other terrestrial systems such as grasslands and woodlands. We will further define agronomic-NOy with field trials of a major UK commercial crop (Triticum), including four cultivars with differing above- and belowground traits. It will be crucial to define NOy soil emissions from these different cultivars, as varying plant traits, such as specific root length, can influence the soil N-cycle microbiome - which will inevitably influence NOy emissions. Other important variables will also be explored, including fertiliser application and spatial variability of NOy flux. Importantly, we will also attempt to determine the role of soil iron and iron speciation on N-cycle community composition and NOy fluxes. Soil iron is an important aspect of our theoretical NOy mechanism - stimulating the production of reactive oxygen species, which is a key reactant in the production of NOy. We will source soil with differing iron content from various farms throughout England to be used in wheat mesocosms studies. Soil NOy fluxes will be measured and connected to mineralogical characteristics and the N-cycle community size. Overall, this project will determine fundamental knowledge on the biogenic production mechanisms of major NOy species, provide direct soil NOy flux measurements from a major global crop, and lead to a better understanding of coupled carbon-nutrient-mineral cycling in soil. Furthermore, this work represents a major step change in the understanding of soil nitrogen dynamics, will be one of the first to couple shotgun metagenomics and culture-dependent methods to atmospheric chemistry processes, and will represent a major advancement in atmospheric accounting of NOy.