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

蚯蚓分泌直径达2毫米的微小碳酸钙颗粒(CaCO3，方解石)。查尔斯·达尔文是最先注意到蚯蚓颗粒产生的人之一，但由于对颗粒所做的研究工作非常少，产生蚯蚓颗粒的原因仍然是一个谜。无论它们为什么形成颗粒，在环境科学中都具有巨大的潜力。它们几乎无处不在地存在于土壤中。目前，正在进行的项目包括碳14测年(坎蒂已经对锡尔伯里山埋藏的土壤表面的方解石颗粒和苔藓进行了测年，并从两者获得了相同的日期)、氨基酸测年(Penkman，约克大学的方解石中的氨基酸外消旋：测定更新世的氨基酸消旋：欢迎博士后奖学金)和U/Th测年(U替代方解石中的钙)(Candy，皇家霍洛韦学院的“一种新的地球年代学方法：蚯蚓方解石的U系列测年”，IP/862/0505，NERC同位素地球科学设施)。颗粒集中在土壤表面，因此坎蒂推测颗粒可以用来识别复杂地层剖面中的化石/埋藏的土壤表面。他还估计方解石的产生率约为2.2毫克/天/只蚯蚓，相当于土壤二氧化碳排放的3%。如果这些速率是正确的，并且颗粒物寿命长，那么颗粒物的产生可能构成新认识的、非常重要的土壤碳循环的一部分，甚至在大气二氧化碳调节中发挥作用。我们如何才能认识到蚯蚓方解石颗粒令人难以置信的潜力？目前，关于它们的形成和寿命，我们还有很多悬而未决的问题。我们试图回答这些基本问题，是什么控制了它们的生产率，它们在土壤中能持续多久？我们的研究将重点放在轮虫身上。它在英国非常常见，发生在从酸性(pH 3.8)到碱性(PH 8)的土壤中。初步工作表明，这种蚯蚓与陆生乳杆菌一起，负责在土壤中产生大部分颗粒。为了确定产量，我们将蚯蚓放在无颗粒土壤中，并在固定的时间段后提取颗粒并称重，从而计算出方解石产量/蚯蚓/时间。我们将使用人造土壤，以确保它最初不含蚯蚓颗粒。土壤将被筛到250微米，这样我们就可以在实验过程中通过再次筛分来提取颗粒250微米。250微米的材料将被收集，制成薄片，并用岩相显微镜进行检查，以定量生产250微米的颗粒。土壤化学将被改变，以确定高和低的pH和Ca含量，以了解这对生产率的影响。用浸泡在不同浓度的硝酸钙溶液中的滤纸喂食蚯蚓，可控制食物中的钙含量。可变土壤化学和可变食品化学实验的结果将使我们能够确定土壤化学和食品化学如何影响颗粒产生率，不同蚯蚓个体之间的颗粒产生率如何变化，以及它如何随时间变化(我们将进行一年的实验，每两个月采样一次)。一旦我们收集到这些实验的颗粒，我们将调查它们在土壤中持续多长时间。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变化和钙浓度的增加，以确定溶解速度。这些速率将与科学文献中方解石溶解的数据进行比较。我们还将在土柱中放置颗粒，并通过方解石颗粒重量随时间的变化来监测溶解情况。这些实验的结果将使我们能够预测方解石颗粒的溶解速度和寿命，以确定它们是否可能足够持久，从而使其同位素分析能够用于古环境研究。

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.