Dissertation Research: Developing Biogeochemical Tracers of Apatite Weathering by Ectomycorrhizal Fungi

磷灰石（存在于大多数土壤中的磷酸钙矿物）是大多数自然生态系统中最重要的磷源。在集中管理的森林中，大量的磷通过采伐被去除，了解磷灰石风化提供磷的速率对于确定这种采伐在没有施肥的情况下是否长期可持续至关重要。有人认为，当生物对磷或钙的需求超过供应时，与树根共生的外生菌根真菌可能能够通过向土壤中释放有机酸来加速磷灰石和其他土壤矿物质的风化。该过程已在受控实验室实验中得到证实，但难以在现场测量。因此，外生菌根风化的模式和重要性在营养胁迫的生态系统知之甚少。本项目将使用磷灰石中的稀土元素（REEs）的浓度升高和铅（Pb）的独特同位素比值来追踪其风化产物。稀土元素和铅同位素浓度将测量从土壤样品中提取的磷灰石，也在外生菌根真菌产生的蘑菇。土壤和蘑菇将收集在八个北方硬木林的立场，氮和磷施肥实验最近开始，不同的土壤磷灰石丰度和林分年龄。这些测量与对比自然和操纵的营养需求和可用性的立场，将提高我们的理解生态系统规模的控制外生菌根风化，真菌的种类负责。这项工作将最终导致改进对不同收获制度和土壤矿物的长期养分供应的估计，从而提高我们可持续管理这些森林的能力。其他更广泛的影响将包括让本科生、国际学生和中学教师参与研究活动。

Apatite (a calcium phosphate mineral present in most soils) is the most important source of phosphorus to most natural ecosystems. In intensively managed forests where large amounts of phosphorus are removed by harvesting, knowing the rate at which phosphorus is supplied by apatite weathering is critical to determining whether such harvesting is sustainable over the long term without fertilization. It has been suggested that when biological demand for phosphorus or calcium exceeds the supply, ectomycorrhizal fungi that grow in a mutualistic relationship with tree roots may be able to accelerate the weathering of apatite and other soil minerals by releasing organic acids into the soil. The process has been demonstrated in controlled laboratory experiments, but is difficult to measure in the field. Thus, the pattern and importance of ectomycorrhizal weathering in nutrient-stressed ecosystems is poorly understood.This project will use the elevated concentrations of rare Earth elements (REEs) and the distinctive isotopic ratios of lead (Pb) in apatite to trace its weathering products. REEs and Pb isotope concentrations will be measured in apatite extracted from soil samples and also in the mushrooms produced by ectomycorrhizal fungi. Soils and mushrooms will be collected at eight northern hardwood forest stands where nitrogen and phosphorus fertilization experiments have recently begun and which differ in soil apatite abundance and stand age. These measurements across stands with contrasting natural and manipulated nutrient demand and availability will improve our understanding of the ecosystem-scale controls on ectomycorrhizal weathering, and the species of fungi responsible. The work will ultimately lead to improved estimates of long-term nutrient supply under different harvest regimes and soil mineralogies, and therefore improve our ability to manage such forests sustainably. Additional broader impacts will include involving undergraduate students, international students, and middle school teachers in research activities.