Iron geochemistry and controls on phosphorus bioavailability in northern peatlands

北极和亚北极泥炭地是高度敏感的生态系统，由于年气温升高，它们正在经历植物覆盖、永久冻土融化和水饱和度的快速变化。这些变化预计会增加有机物的分解并释放温室气体。植物生长可以通过光合作用将碳封存在陆地生态系统中，并在短时间内减缓碳向大气的释放，但植物生长增加抵消土壤碳损失的能力因土壤养分有效性而变得复杂。特别是，当需求超过目前的供应时，关键养分磷可能越来越限制植物生长；然而，对磷生物有效性的非生物控制仍然是北方泥炭地的一个主要知识缺口。这项研究将调查高纬度土壤中磷生物有效性的地球化学控制，以评估冻土带和北方生态系统作为大气温室气体未来汇的潜力。该项目将在一个敏感和动态的生态系统中为研究生和本科生提供研究培训。调查人员和他们的学生还将通过在克利夫兰自然历史博物馆开展一个关于土壤的教育项目，参与社区外展活动。他们将通过实践活动向K-6年级的学生及其家人讲授北极土壤、土壤多样性以及土壤作为自然资源的重要性。具体来说，pi将探索这样一个假设，即在不断变化的水文制度下，在富铁泥炭地广泛排水过程中，磷被低结晶铁氢氧化物吸附而迅速沉淀，会加剧高纬度地区的磷限制。由于与氧化铁矿物的氧化还原依赖相互作用，植物磷的有效性受到水文条件的强烈调节。干燥土壤中铁结合磷的增加可能导致磷限制，从而限制植物生长和限制植物生物量的碳储存。本研究的目的是将地球化学分析（例如，铁和磷的耦合提取）与同步源光谱相结合，以评估阿拉斯加泥炭地实验（APEX）中淹水至排水良好的土壤在实验操纵梯度上铁和磷之间的地球化学关联。从冻土带（如图里克湖、巴罗环境观测站）和北方泥炭地（如马塞尔实验森林）的长期观测站获得的土壤的额外地球化学分析将为本研究提供更广泛的背景。

Arctic and subarctic peatlands are highly sensitive ecosystems that are experiencing rapid changes in plant cover, permafrost thaw, and water saturation due to increasing annual temperatures. These changes are expected to increase organic matter decomposition and release greenhouse gases. Plant growth may sequester carbon in terrestrial ecosystems via photosynthesis and mitigate releases to the atmosphere over short time-scales, but the ability of increased plant growth to offset soil carbon losses is complicated by soil nutrient availability. In particular, the critical nutrient phosphorus may become increasingly limiting to plant growth as demand exceeds current supply; however, non-biological controls on phosphorus bioavailability remain a major knowledge gap for northern peatlands. This research will investigate geochemical controls on phosphorus bioavailability in high-latitude soils to evaluate the potential for tundra and boreal ecosystems to act as future sinks for atmospheric greenhouse gasses. The project will provide graduate and undergraduate students with research training in a sensitive and dynamic ecosystem. The investigators and their students will also engage in community outreach by running an educational program on soils at the Cleveland Museum of Natural History. They will use hands-on activities to teach K-6 students and their families about Arctic soils, soil diversity, and the importance of soil as a natural resource.Specifically, the PIs will explore the hypothesis that phosphorus limitation at high-latitudes will be exacerbated by phosphorus adsorption to poorly-crystalline iron oxyhydroxides that rapidly precipitate during widespread drainage of iron-rich peatlands under changing hydrologic regimes. Phosphorus availability to plants is strongly regulated by hydrologic conditions due to redox-dependent interactions with iron oxyhydroxide minerals. Increases in iron-bound phosphorus in drying soils may lead to phosphorus limitation that constrains plant growth and limits carbon storage in plant biomass. The objective of this research is to integrate geochemical analyses (e.g., coupled iron and phosphorus extractions) with synchrotron-source spectroscopy to evaluate geochemical associations between iron and phosphorus across an experimentally-manipulated gradient of flooded to well-drained soils at the Alaska Peatland Experiment (APEX). Additional geochemical analysis of soils obtained from long-term observatories in tundra (e.g., Toolik Lake, Barrow Environmental Observatory) and boreal peatlands (e.g., Marcell Experimental Forest) will provide broader context for this study.