Experimental constraints on contributions of mycorrhizal symbioses to bedrock weathering of calcium and magnesium

智力优势：虽然众所周知，生物体对大陆环境中的风化过程和元素分布有重要贡献，但不同生物体对镁和钙等关键元素循环的相对影响仍然知之甚少。菌根共生已被认为是陆地生态系统中元素循环的重要组成部分，其中丛枝菌根真菌在农田、热带和一些温带地区占优势，外生菌根真菌在温带和北方森林中占优势。然而，这些共生体在风化中的作用以及它们的存在对镁和钙等关键元素循环的影响尚未量化。为了解决这些问题的定量和系统的方式，我们进行了一系列的培养实验的松树和枫树幼苗，生长不同的真菌共生体和花岗岩和碳酸盐岩基岩层。通过这项工作，我们将确定真菌群落对风化过程的影响以及元素和同位素的生物和地球化学分馏的程度。我们的实验将使我们能够评估：（1）丛枝（枫树）与外生菌根（松树）共生体对风化的相对意义（2）真菌生物量与风化作用的关系，（3）养分供应速率对风化作用的影响，（4）叶化学中基岩类型记录的真实性，（5）土壤中微生物的数量与风化作用的关系，（6）土壤中微生物的数量与风化作用的关系，（7）土壤中微生物的数量与风化作用的关系。（5）重要元素和重要同位素循环的关键地球化学贡献。我们将评估这些问题，通过结合使用的微量元素和同位素分析的基岩渗滤液，基岩digestion，净化液，和生物组织（真菌，根，茎和叶）。我们特别感兴趣的是使用这些实验来阐明生物的钙和镁同位素循环，两个最重要的新兴同位素系统，需要在不同的地球表面和生态系统水库的元素预算的贡献。这些系统中一个关键的悬而未决的问题仍然是确定同位素分馏沿着生物和非生物途径。基于文献和对松树幼苗钙同位素系统学的初步研究，我们假设钙和镁都将在生物组织中进行生物分馏，树木组织的同位素特征反映了非生物和生物分馏的机制。我们将开发的综合数据集将最终提高我们对陆地储层内元素循环的理解，并提供感兴趣的结果，地球科学界的几个部分，包括研究水文学、生物地球化学、生态系统内的地球化学循环以及大陆对海洋地球化学循环的贡献的部分。拟议的工作将形成博士学位的最后章节。一位有前途的早期职业女性地球化学家的论文。此外，拟议的研究继续并进一步加强UNH小组与比利时哈瑟尔特大学和美国地质调查局的科学家之间富有成效的跨学科合作。这项合作将加强UNH地球化学的研究计划和实验室发展。PI与高中教师和高中学生就与拟议研究有关的主题积极合作，研究结果将广泛发表并纳入UNH地球化学课程。

Intellectual Merit: Although it is well known that organisms contribute significantly to the weathering process and to the distribution of elements within continental environments, the relative influence of different organisms on key elemental cycles such as magnesium and calcium remain poorly understood. Mycorrhizal symbioses have been recognized as important parts of elemental cycles within terrestrial ecosystems, with arbuscular mycorrhizal fungi dominant in croplands, the tropics, and some temperate regions, and ectomycorrhizal fungi dominant in temperate and boreal forests. The role of these symbioses, however, in weathering and the influence of their presence on key elemental cycles such as magnesium and calcium are not quantified. To address these questions in a quantitative and systematic way, we have carried out a series of culture experiments of pine and maple seedlings, grown with different fungal symbionts and supplied with granitic and carbonate bedrock layers. With this work, we will identify the influence of fungal communities on the weathering process and the magnitude of biological and geochemical fractionation of elements and isotopes. Our experiments will enable us to assess: (1) the relative significance of arbuscular (maple) versus ectomycorrhizal (pine) symbioses on weathering (i.e. bedrock mineral dissolution); (2) the links between the abundance of fungal biomass with weathering; (3) the influence of nutrient supply rate on weathering; (4) the fidelity of the record of bedrock type in foliar chemistry; and (5) key biogeochemical contributions to important elemental and important isotopic cycles. We will assess these questions through the combined use of trace elements and isotope analyses of bedrock leachate solutions, bedrock digestions, percolating fluids, and biological tissues (fungi, roots, stems and foliages). We are specifically interested in using these experiments to elucidate biological contributions to the calcium and magnesium isotope cycles, two of the most important emerging isotope systems requiring elemental budgets within different Earth surface and ecosystem reservoirs. One key outstanding question within these systems remains the identification of isotope fractionation along biological and abiotic pathways. Based on the literature and preliminary studies of calcium isotope systematics in pine seedlings, we hypothesize that calcium and magnesium will both be biologically fractionated within the biological tissues, and that the isotopic signatures of the tree tissues reflect mechanisms of both abiotic and biotic fractionation.Broader Impacts: The integrated dataset we will develop will ultimately improve our understanding of element cycling within terrestrial reservoirs and provide results that will be of interest to several segments of the earth sciences community, including those studying hydrology, biogeochemistry, geochemical cycling within ecosystems, and continental contributions to marine geochemical cycles. The proposed work will form the final chapters of a Ph.D. dissertation of a promising early career female biogeochemist. Additionally, the proposed study continues and further strengthens productive interdisciplinary collaborations between the UNH group and scientists from Hasselt University in Belgium and the U.S. Geological Survey. This collaboration will enhance the research program and laboratory development in biogeochemistry at UNH. The PIs actively work with high school teachers and high school students on topics related to the proposed studies, and the research results will be published widely and incorporated into the UNH geochemistry curriculum.