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

大气活性氮氧化物气体（NOy = NO + NO2 + HONO +…）通过人类活动（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氮循环耦合。传统认为土壤氮排放的生物地球化学以氮气（N2）和氧化亚氮（N2O）为主；然而，卫星、模型和实验室研究表明，土壤中NOy的排放量可能比这些更常见的测量氮气的排放量更大。NOy作为臭氧（O3）的前体在大气化学中具有重要意义，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，尤其是在青少年和老年人中。除了人为来源外，NOy气体还来自自然非点源，包括土壤（占NOy总排放量的24%）、野火（19%）和闪电（13%）。然而，人们对这些自然来源的NOy通量知之甚少，尽管它们占大气中NOy总量的50%——随着车辆和工业排放的持续下降，这一比例还在增加。重要的是，关于生物源（微生物源）产生机制的信息严重缺乏，导致noy耦合气候模式预测不准确。这主要是由于对二氧化氮（NO2）和亚硝酸（HONO）等主要NOy物种的形成缺乏了解。我们怀疑存在尚未发现的noy产生途径，由来自所有三个生命领域的大量微生物催化。我们的假设机制来源于人类生理学，其中NOy物种是已知的重要信号分子。我们将在农业土壤中探索这些机制，因为土壤是NOy气体的最大天然来源，并且在农业背景下，我们的初步工作表明，这些土壤比其他陆地系统（如草地和林地）产生更多的NOy。我们将通过一种主要的英国商业作物（小麦）的田间试验进一步定义农艺noy，包括四个具有不同地上和地下性状的品种。确定这些不同品种的土壤NOy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，包括肥料施用和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NOy理论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，用于小麦中生态系统研究。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，该项目将确定主要NOy物种生物成因生产机制的基础知识，提供来自全球主要作物的直接土壤NOy通量测量，并更好地了解土壤中碳-营养-矿物耦合循环。此外，这项工作代表了对土壤氮动力学理解的重大变化，将是第一个将鸟枪宏基因组学和培养依赖方法与大气化学过程结合起来的研究之一，并将代表NOy大气计算的重大进展。

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.