Impact of soil chemistry and diet on rates of calcite production by the earthworm Lumbricus rubellus.

蚯蚓排泄出直径达2毫米的微小碳酸钙颗粒（CaCO3，方解石）。查尔斯达尔文是最早注意到颗粒生产的人之一，但由于对颗粒的研究工作量非常小，其生产原因仍然是一个谜。无论它们为什么形成颗粒，在环境科学中都有巨大的潜力。它们在土壤中几乎无处不在。目前，正在进行的项目正在研究其碳14测年的潜力（Canti从Silbury Hill的一个埋藏的土壤表面测定了方解石颗粒和苔藓的年代，并从两者中获得了相同的日期），氨基酸年代测定（Penkman，约克大学的"方解石中的氨基酸外消旋：更新世的年代测定（博士后奖学金）和U/Th年代测定（U取代了方解石中的Ca）（Candy，皇家霍洛威学院"第四纪陆地年表的新方法：方解石的U系列定年" IP/862/0505，NERC同位素地球科学设施）。颗粒集中在土壤表面，因此Canti推测颗粒可以用来识别复杂地层剖面中的化石/埋藏土壤表面。他还估计了C的方解石生产率。2.2 mg/day/kg，相当于土壤CO2排放量的3%。如果这些速率是正确的，颗粒是长寿命的，那么颗粒生产可能构成一个新的认识，土壤碳循环的高度重要的一部分，甚至在大气中的CO2调节中发挥作用。我们如何才能实现方解石颗粒令人难以置信的潜力？目前，我们有很多关于它们的形成和寿命的未解之谜。我们试图回答基本的问题，是什么控制他们的生产率和他们在土壤中持续多久？本研究以红蚯蚓为研究对象。它在英国非常常见，存在于酸性（pH 3.8）至碱性（pH 8）的土壤中。初步工作表明，这一点，连同L。terrestris是负责生产土壤中的大部分颗粒。为了确定生产率，我们将蚯蚓保持在颗粒自由土壤中，并在固定时间段后提取和称重颗粒，从而计算方解石生产量/单位/时间的生产率。我们将使用人造土壤，以保证它最初没有颗粒。在实验过程中，通过再次筛分土壤，将土壤筛分至250 um。<250um so that we can extract granules >将收集&lt;250 μ m的材料，制成薄切片，并用岩相显微镜检查，以量化产生的&lt;250 μ m的颗粒。土壤化学将被改变，以提供高和低的pH值和钙含量，看看这如何影响生产率。用不同浓度的硝酸钙溶液浸泡滤纸，饲喂蚯蚓，控制饲料中钙的含量。可变土壤化学和可变食物化学实验的结果将使我们能够确定土壤化学和食物化学如何影响颗粒生产率，颗粒生产率如何在不同的玉米个体之间变化以及如何随时间变化（我们将运行我们的实验一年，每2个月采样一次）。一旦我们从这些实验中收集到颗粒，我们将研究它们在土壤中持续多久。我们将通过反应器实验进行流动，将颗粒溶解在酸中，并监测pH值变化和Ca浓度的增加，以确定溶解速率。这些速率将与方解石溶解的科学文献中的数据进行比较。我们还将把颗粒放在土柱中，并通过方解石颗粒重量随时间的变化来监测溶解。这些实验的结果将使我们能够预测方解石颗粒的溶解速率和寿命，以确定它们是否可能足够长的时间来进行同位素分析，以用于古环境研究。

Earthworms excrete tiny calcium carbonate granules (CaCO3, calcite) up to 2mm in diameter. Charles Darwin was one of the first people to notice earthworm granule production but due to the remarkably small amount of research work that has been done on granules reasons for their production remain a mystery. Regardless of why they form granules have great potential in environmental science. They are found almost ubiquitously in soils. Currently there are ongoing projects looking at their potential for carbon 14 dating (Canti has dated calcite granules and moss from a buried soil surface at Silbury Hill and obtained the same dates from both), amino-acid dating (Penkman, York University 'Amino-acid racemization in calcite: Dating the Pleistocene' Welcome Postdoctoral Fellowship) and U/Th dating (U replaces the Ca in the calcite) (Candy, Royal Holloway College 'A new approach to Quaternary terrestrial chronologies: U-series dating of earthworm calcite' IP/862/0505, NERC ISOTOPE GEOSCIENCE FACILITIES). Granules concentrate at soil surfaces so Canti has speculated granules could be used to identify fossil / buried soil surfaces in complex stratigraphic sections. He also estimated calcite production rates of c. 2.2 mg/day/earthworm, equivalent to 3% of the CO2 flux from soil. If these rates are correct and granules are long lived then granule production could constitute a newly recognized, highly significant part of the soil C cycle and even play a role in atmospheric CO2 regulation. How can we realize the incredible potential of earthworm calcite granules? At present we have lots of unanswered questions about their formation and longevity. We seek to answer the basic questions, what controls their production rate and how long do they last in soil? Our study will focus on Lumbricus rubellus. It is very common in the UK, occurring in soils ranging from acid (pH 3.8) to alkali (pH 8). Preliminary work shows this earthworm, together with L. terrestris, is responsible for producing the majority of granules in soils. To determine production rate we will keep earthworms in granule free-soil and extract and weigh granules after fixed time periods thus calculating production rates of mass of calcite produced / earthworm / time. We will use artificial soil in order to guarantee it is initially free from earthworm granules. The soil will be sieved to <250um so that we can extract granules >250um over the course of the experiment by sieving the soil again. The <250um material will be collected, made into thin sections, and examined with a petrographic microscope to quantify granules produced that are <250um. Soil chemistry will be altered to give high and low pH and Ca content to see how this effects production rate. Ca content of food will be controlled by feeding the earthworms on filter paper soaked in different strengths of Ca nitrate solution. Results from the variable soil chemistry and the variable food chemistry experiments will allow us to determine how soil chemistry and food chemistry affect granule production rate, how granule production rate varies between different earthworm individuals and how it varies over time (we will run our experiments for a year, sampling every 2 months). Once we have a collection of granules from these experiments we will investigate how long they last in soils. We will carry out flow through reactor experiments, dissolving granules in acid and monitoring pH change and increase in Ca concentration to determine dissolution rates. These rates will be compared to data in the scientific literature for calcite dissolution. We will also put granules in soil columns and monitor dissolution through the change in calcite granule weight over time. Results from these experiments will allow us to predict dissolution rates and longevity of the calcite granules to determine whether they are likely to be sufficiently long lasting for their isotopic analysis to be of use in palaeoenvironmental studies.