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QUANTIFYING THE BIOMOLECULAR FATE OF DIETARY C AND N IN EARTHWORM TISSUES AND CASTS

量化膳食 C 和 N 在蚯蚓组织和粪中的生物分子命运

基本信息

批准号：
NE/F011431/1
负责人：
Richard Evershed
金额：
$ 5.39万
依托单位：
University of Bristol
依托单位国家：
英国
项目类别：
Research Grant
财政年份：
2008
资助国家：
英国
起止时间：
2008 至无数据
项目状态：
已结题

来源：
https://gtr.ukri.org/projects?ref=NE%2FF011431%2F1
关键词：
QUANTIFYING BIOMOLECULAR FATE DIETARY EARTHWORM

项目摘要

The importance of earthworms in the processing of soil organic matter (OM) was recognised by such illustrious scholars as Aristotle, who described them as 'the intestines of the Earth', and Charles Darwin who introduced the concept of earthworms as 'Nature's plough'. Nowadays, the capacity of earthworms to modify the distribution of organic compounds through the excavation of soils has led them to be described as 'soil engineers'. Their feeding activity in soils is widely recognised as beneficial, and results in increased soil quality through the addition of plant nutrients to mineral soil horizons and improved water retention, aeration, stability and workability. These improvements enhance root growth and increase biodiversity of soil fauna. Earthworms use soil organic matter, such as dead plant material, as a food source. Earthworms pull organic matter down into burrows, or simply eat it and subsequently deposit it in worm casts (their faeces) at or below the soil surface. During ingestion they transform their diet into small fragments. Some of these are digested and contribute to the earthworm's body mass, the rest being excreted in worm casts and mucus excretions. Surprisingly, it is unknown which components of organic matter earthworms eat, how much is absorbed into their body mass, and how much and which parts of their diet are excreted back into the soil. To find out which parts of organic matter earthworms eat, absorb and excrete, we are going to feed a common grassland, litter-feeding species of earthworm with 13C- and 15N-labelled ryegrass in soil mesocosms. 13C and 15N are naturally occurring non-radioactive stable isotopes of carbon and nitrogen that exist in much lower abundances in the atmosphere than the most abundant isotopes, 12C and 14N. The ratio between 13C:12C and 15N:14N can be calculated using isotope ratio mass spectrometry. The ryegrass for the experiment will be grown in sealed growth chambers: CO2 gas containing a high proportion of 13C will be supplied for photosynthesis, and nitrate (NO3-) containing a high proportion of 15N will be supplied in solution to the roots, producing 13C- and 15N-labelled plant material. When the earthworms eat the grass, the nutrients they absorb into their bodies, and then excrete as respired gas, mucus and casts, will also be labelled with 13C and 15N. We will extract different substances from the cuticle, muscle tissue, mucus and casts of the earthworms, and also from the remaining ryegrass and soil, to work out how much of the labelled substances have been utilised by the earthworms. We will also sample CO2 from the mesocosms to see how much of the diet has been used for energy production. By measuring how much of the 13C and 15N label has been incorporated into all of these samples, we will be able to calculate how much protein, carbohydrate and fat from the grass has been processed by the earthworm. Importantly, we will also be able to determine precisely if and how earthworms cause greater release (priming) or storage (sequestration) of carbon and nitrogen from organic matter in soils. Overall, this research will add a new dimension to the understanding of how earthworms affect the breakdown of organic matter, how much organic matter they can process, and whether their activity increases or decreases the amount of carbon and nitrogen stored in the soil.

亚里士多德和查尔斯·达尔文等杰出学者都认识到蚯蚓在处理土壤有机质（OM）方面的重要性，他将蚯蚓描述为“地球的肠子”，查尔斯·达尔文则提出了蚯蚓为“自然犁”的概念。如今，蚯蚓通过挖掘土壤来改变有机化合物分布的能力使它们被称为“土壤工程师”。它们在土壤中的取食活动被广泛认为是有益的，并通过向矿质土壤层添加植物养分并改善保水性、通气性、稳定性和和易性来提高土壤质量。这些改进促进了根系生长并增加了土壤动物的生物多样性。蚯蚓利用土壤有机物（例如死去的植物材料）作为食物来源。蚯蚓将有机物拉入洞穴，或者只是吃掉它，然后将其沉积在土壤表面或土壤表面以下的蠕虫排泄物（它们的粪便）中。在摄入过程中，它们将饮食转化为小碎片。其中一些被消化并增加了蚯蚓的体重，其余的则以蠕虫粪便和粘液排泄物的形式排出。令人惊讶的是，目前尚不清楚蚯蚓吃有机物的哪些成分，有多少被吸收到它们的身体质量中，以及它们饮食中的多少和哪些部分被排泄回土壤中。为了找出蚯蚓吃、吸收和排泄有机物的哪些部分，我们将在土壤中层世界中用 13C 和 15N 标记的黑麦草喂养一种常见的草地、以垫料为食的蚯蚓。 13C 和 15N 是天然存在的碳和氮的非放射性稳定同位素，其在大气中的丰度比最丰富的同位素 12C 和 14N 低得多。 13C:12C 和 15N:14N 之间的比率可以使用同位素比质谱法计算。实验用的黑麦草将在密封的生长室中生长：含有高比例13C的CO2气体将被供应用于光合作用，含有高比例15N的硝酸盐（NO3-）将以溶液形式供应至根部，产生13C和15N标记的植物材料。蚯蚓吃草时，吸收到体内的营养物质，然后以呼吸气体、粘液和管型的形式排出体外，也会被标记为13C和15N。我们将从蚯蚓的角质层、肌肉组织、粘液和管型中，以及剩余的黑麦草和土壤中提取不同的物质，计算出有多少标记物质被蚯蚓利用了。我们还将从中宇宙中取样二氧化碳，看看有多少饮食被用于能量生产。通过测量所有这些样本中含有多少 13C 和 15N 标签，我们将能够计算出蚯蚓处理了多少草中的蛋白质、碳水化合物和脂肪。重要的是，我们还能够准确确定蚯蚓是否以及如何导致土壤中有机物更多地释放（启动）或储存（封存）碳和氮。总体而言，这项研究将为了解蚯蚓如何影响有机物的分解、它们可以处理多少有机物，以及它们的活动是否增加或减少土壤中储存的碳和氮量增加了一个新的维度。