N isotope heterogeneity in soil organic matter: a new tool to characterise N cycles

土壤有机质中的氮同位素异质性：表征氮循环的新工具

• 批准号: BB/E006663/1
• 负责人: David Manning
• 金额: $ 11.85万
• 依托单位: Newcastle University
• 依托单位国家: 英国
• 项目类别: Research Grant
• 财政年份: 2007
• 资助国家: 英国
• 起止时间: 2007 至 无数据
• 项目状态: 已结题
• 来源: https://gtr.ukri.org/projects?ref=BB%2FE006663%2F1
• 关键词: isotope; heterogeneity; soil; organic; matter

Nitrogen turnover is an essential part of the plant-soil system. Organic N, within dead plant tissue or other biological products, is not available for plant uptake until it has been mineralised. Differing soil organic matter pools have different stabilities, and so N in soils rich in reactive soil organic matter (SOM) is much more rapidly mineralised than that in soils with stable SOM. In each case, the bulk chemistry of the organic matter differs, with implications for the chemistry and availability of N. In reactive SOM, amine N is readily available for mineralisation. In stable SOM, aromatic and related C compounds exist, and N within aromatic ring structures is much less readily mineralised. Models of N turnover allocate measured N to pools with differing stability. At present these are not rigorously related to direct measurements of the N content of discrete SOM pools. Our proposal develops a tool to achieve this. We have shown that SOM loses N in different gaseous forms as it is heated by temperature-programmed combustion in a thermal analysis system. Initially, reduced (cyanide-based) gases are evolved from the decomposition of aliphatic SOM. N oxides are then evolved as aromatic compounds break down. This chemical heterogeneity reflects differing structural hosts for N within SOM, which are measured from observed weight losses. We observe C isotope heterogeneity between these hosts, begging the question that natural abundances of N isotopes also vary. Our proposal is to build a completely new combination of instrumentation, linking existing thermal analysis and stable isotope instrumentation via a novel interface that is capable of taking different N gases from the thermal analysis machine (which gives a continuous record of weight loss, hence proportions of discrete components) and presenting them to the isotope ratio mass spectrometer for determination of N isotope ratios. It will then be possible to use N isotope fingerprints to track nitrogen turnover, in fertiliser-soil-plant systems. This system will provide for the first time a tool to investigate chemical and natural/labelled isotopic heterogeneity for N within soil organic matter, enabling N turnover models to be related to measurable parameters from agricultural soils.

氮更新是植物土壤系统的重要组成部分。有机n在死亡植物组织或其他生物产品中，直到被矿化为止，才可用于植物摄取。不同的土壤有机物池具有不同的稳定性，因此在富含反应性土壤有机物（SOM）的土壤中，n比稳定的SOM的土壤矿物质较快。在每种情况下，有机物的批量化学都不同，对n的化学和可用性的影响。在反应性SOM中，胺N很容易用于矿化。在稳定的SOM中，存在芳香族和相关的C化合物，芳环结构内的n很容易矿化。 n个周转率的模型分配了n个n的n，其稳定性不同。目前，这些与离散SOM池的N含量的直接测量无关。我们的建议开发了实现这一目标的工具。我们已经表明，SOM以不同的气态形式丢失N，因为它在热分析系统中被温度填充加热。最初，从脂肪族SOM的分解中进化了降低的（基于氰化物的）气体。然后随着芳香族化合物的分解而进化n氧化物。这种化学异质性反映了SON内N的不同结构宿主，这是根据观察到的体重减轻来测量的。我们观察到这些宿主之间的C同位素异质性，乞求一个问题，即N同位素的自然丰度也有所不同。我们的建议是通过新型界面链接现有的热分析和稳定的同位素仪器的全新组合，该界面能够从热分析机器中吸收不同的N气体（这使体重减轻的连续记录，因此离散成分的比例连续记录）并将其显示为同位素比率质量分析仪以确定N ISOTOPE率的同位比率。然后，在受精蛋白 - 土壤植物系统中，可以使用N同位素指纹跟踪氮更新。该系统将首次提供一种研究土壤有机物内N的化学和天然/自然/标记的同位素异质性的工具，从而使N周转模型与农业土壤的可测量参数有关。