Do microbe-mineral interactions influence nitrogen cycle dynamics?

土壤中的大部分有机氮通常存在于土壤的矿物相关有机质（MAOM）部分，其周转率较慢，并且被认为微生物和植物在很大程度上无法进入（Cotrufo et al. 2013）。部分分解的植物物质构成土壤中的颗粒有机质（POM）部分，通常占总有机氮的比例较小，因此，MAOM可以被视为根际N有效性的瓶颈，其N矿化率取决于有机质的结构及其与土壤矿物质和微生物群落的相互作用。该项目的潜在目标是研究生态系统-微生物-矿物相互作用如何驱动土壤中的氮氧化物通量。虽然已经很好地量化了生态系统中氧化亚氮的通量，但由于活性性很强，对活性氮氧化物的通量的研究很少。我们对控制这些通量的因素的不完全了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。我们的目标是揭示自然生态系统（主要是林地和草原）中决定氮氧化物通量的因素，采用将现场实验与最先进的分析能力和宏基因组分析相结合的方法。N2O和NOy通量都将被量化，以更好地确定对两者负责的土壤因子及其潜在的相互作用。我们的假设是氮氧化物排放受三个因素控制：i)土壤微生物的活动将根据生态系统、POM和MAOM的比例以及土壤矿物学而变化。为了验证我们的假设，我们将：(1)通过田间试验确定土壤矿物学和土壤有机质组成对土壤氮氧化物放气的影响；(2)确定不同土壤组分和不同生态系统中som -矿物相互作用对氮有效性和矿化率的影响；(3)确定哪些土壤组分是采氮微生物的目标，哪些分类群在这些组分中产生调动氮所需的酶。

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.