Do microbe-mineral interactions influence nitrogen cycle dynamics?

土壤中的大多数有机氮通常存在于土壤的矿物质相关有机质(MAOM)部分中，这一部分的周转速度很慢，被认为在很大程度上无法被微生物和植物获取(Cotrufo等人)。2013)。部分分解的植物物质构成了土壤中的颗粒有机质(POM)，其在总有机氮中所占的比例通常较小。因此，MAOM可以被视为根际N有效性的瓶颈，N的矿化速率取决于有机质的结构及其与土壤矿物和微生物群落的相互作用。该项目的基本目标是调查生态系统-微生物-矿物相互作用如何推动土壤中的氮氧化物通量。虽然已经很好地量化了来自生态系统的一氧化二氮通量，但由于活性氮氧化物的高活性性质，对其通量的研究很少。我们对控制这些通量的因素的不完全理解限制了我们预测土壤氮排放对空气质量和气候影响的能力。我们的目标是揭示决定自然生态系统(主要是林地和草原)氮氧化物通量的因素，采用一种将实地实验与最先进的分析能力和元基因组分析相结合的方法。将对N2O和NOY通量进行量化，以更好地确定导致这两种通量的土壤因素及其潜在的相互作用。我们的假设是，氮氧化物的排放受三个因素控制：i)土壤微生物的活动将随生态系统、POM和MAOM的比例以及土壤矿物学的不同而变化。为了验证我们的假设，我们将：(1)在田间试验中确定土壤矿物学和土壤有机质组成对土壤氮氧化物排放的关系；(2)确定不同土壤组分和不同生态系统中SOM-矿物相互作用如何影响N的有效性和矿化速率；(3)确定哪些土壤组分是N采矿微生物的靶标，哪些分类群产生动员这些组分中N所需的酶。

The majority of organic N in soil is often held in the mineral-associated organic matter (MAOM) fraction of soil, which has slow turnover rates and is thought to be largely inaccessible to microbes and plants (Cotrufo et al. 2013). Partially decomposed plant material constitutes the particulate organic matter (POM) fraction in soil, which typically holds a smaller proportion of total organic N. Thus, MAOM can be viewed as a bottleneck to N-availability within the rhizosphere, with N mineralization rates depending on the structure of organic matter and its interaction with soil minerals and microbial communities. The underlying goal of this project is to investigate how ecosystem-microbe-mineral interactions drive nitrogen oxide fluxes from soils. While fluxes of nitrous oxide have been well quantified from ecosystems, fluxes of reactive nitrogen oxides are poorly studied owing to their highly reactive nature. Our incomplete understanding of the factors that control these fluxes has limited our ability to predict the air quality and climate impacts of soil N emissions. We aim to uncover the factors that determine nitrogen oxide fluxes in natural ecosystems (primarily woodlands and grasslands), using an approach that combines field experiments with state-of-the-art analytical capabilities and metagenomic analyses. Both N2O and NOy fluxes will be quantified to better determine edaphic factors responsible for both, and their potential interactions. Our hypothesis is that nitrogen oxide emissions are controlled by three factors: i) the activities of soil microbes that will vary depending on the ecosystem, the proportion of POM and MAOM, and the underlying soil mineralogy. To test our hypothesis, we will: (1) Determine the relationship between soil mineralogy and soil organic matter composition on soil outgassing of nitrogen oxides in field experiments; (2) determine how SOM-mineral interactions affect N availability and mineralization rates in different soil fractions and in varying ecosystems; (3) determine which soil fractions are targeted by N-mining microbes and which taxa produce the enzymes needed to mobilize N in those fractions.