LTREB: Collaborative Research: Long-term changes in peatland C fluxes and the interactive role of altered hydrology, vegetation, and redox supply in a changing climate

全球重要的碳(C)储存在北方（北方）泥炭地容易受到降水和径流模式改变、地下水输入以及高纬度地区冻土（称为“永久冻土”或“冰冻圈”）范围变化的影响。这些变化可以影响北方湿地的范围，以及它们吸收和转化碳和其他营养物质的能力。2005年，阿拉斯加泥炭地实验（APEX）成立，旨在研究土壤气候和植被变化对泥炭地碳循环的作用。在过去15年中，已经收集了关于土壤湿度和温度、植物组成和数量以及模拟洪水和干旱的地下水位处理所排放的重要大气气体（如甲烷和二氧化碳）的通量的核心数据。该小组先前调查的一个关键结果是，无论地下水位位置如何，该实验地点的碳排放量似乎很高，这表明植物物种组成变化之间的相互作用对处理的响应强烈地控制了该生态系统保持碳的能力。这是环境生物学长期研究（LTREB）项目（DEB-1354370）的五年更新。该研究正在研究水文变化、植物物种组成和气候变化（特别是洪涝和干旱）在控制泥炭地碳储量方面的相互作用；这项工作对于理解气候变化对碳循环过程的影响是必要的。本科生、研究生和博士后研究人员都将接受现场和实验室技术方面的培训。研究结果也将被纳入新的高中课程，用于促进科学夏令营。目前泥炭地碳循环的观点是，大部分土壤碳矿化发生在地下水位以上相对较浅的曝气泥炭层（acrotelm），而发生在缺氧层（catotelm）的深层泥炭碳分解最少。因此，地下水位的位置（以及与之相关的acrotelm厚度）被用作总体分解率和长期泥炭积累率的预测指标。然而，该团队对阿拉斯加泥炭地地下水位位置进行了15年的操纵（阿拉斯加泥炭地实验，APEX），结果挑战了这一观点，特别是表明饱和泥炭中的碳矿化速度比先前预期的要快，导致厌氧二氧化碳产量高通量。先前的分析表明，地下水位位置对生态系统呼吸没有显著影响，但这一结果可能至少部分归因于在较低（干燥）和较高（湿润）地下水位位置下发生的植被变化。最初的实验设计不能区分水文植被变化对泥炭氧化还原和碳通量的影响。因此，了解变化的水文和植被对厌氧分解过程的相互作用，以及这如何控制泥炭地深层土壤C库的周转，是LTREB资助第一阶段的主要目标。结果表明，在LTREB资助初期，莎草和木贼根际确实对泥炭和溶解有机质具有氧化作用。然而，这一研究期间的持续洪水暴露了对该系统中微量气体产生控制机制的关键理解空白，并揭示了植物群落结构和藻类的优势可能对土壤氧化还原过程和碳通量具有独特的控制作用。洪水历史对藻类和异养微生物的相对活性也有很强的控制作用，这取决于来自不同植物的C底物的变化。确切地说，植物群落的变化如何与改变的地下水位相互作用，以控制电子供体和受体的供应，以及这如何控制低水位和高水位年份的厌氧代谢，是这个合作团队将在未来五年内研究的关键问题。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Globally important carbon (C) stores in northern (boreal) peatlands are vulnerable to changes in altered precipitation and runoff patterns, groundwater inputs, and changes in the extent of frozen ground in high latitudes (called ‘permafrost’, or the ‘cryosphere’). These changes can affect the extent of boreal wetlands as well as their ability to sequester and transform C and other nutrients. In 2005, the Alaska Peatland Experiment (APEX) was created to examine the role of changing soil climate and vegetation on peatland C cycling. Over the past fifteen years, core data has been collected on soil moisture and temperature, plant composition and amount, and the fluxes of important atmospheric gases emitted (as methane and carbon dioxide) from water table treatments that simulate floods and droughts. A key result from this group's prior investigations was that C emissions from this experimental site appeared to be high, regardless of water table position, revealing that interactions among changes in plant species composition in response to the treatments were strongly controlling the ability of this ecosystem to retain C. This is a five-year renewal of a Long-Term Research in Environmental Biology (LTREB) project, DEB-1354370. The study is examining the interactions among changes in hydrology, plant species composition and changes in climate (particularly flooding and drought) in controlling C storage in this peatland complex; this work is necessary for understanding the consequences of an altered climate for C cycle processes. Undergraduates, graduate students and post-doctoral researchers will all be trained and in field and laboratory techniques. Results from the research will also be incorporated into new high school curricula for use in the Fostering Science summer camp.The current view of peatland carbon cycling is that the majority of soil carbon mineralization occurs in the relatively shallow aerated peat layer above the water table (acrotelm), and that deeper peat carbon occurring in anoxic layers (catotelm) undergoes minimal decomposition. As such, the position of the water table (and the associated thickness of the acrotelm) is used as a predictor of overall decomposition rates and long-term peat accumulation rates. However, findings from this team's fifteen-year manipulation of water table position in an Alaskan fen (Alaska Peatland Experiment, APEX) challenge this view, and in particular suggest that carbon mineralization in saturated peat is faster than previously expected, leading to high fluxes of anaerobic CO2 production. Prior analyses indicated no significant effect of water table position on ecosystem respiration, but it is possible that this result was due at least partially to changes in vegetation that have occurred both under lower (drier) and higher (wetter) water table positions. The initial experimental design could not disentangle the effects of changes in vegetation from hydrology on peat redox and C fluxes. As such, understanding the interactive effects of altered hydrology and vegetation on anaerobic decomposition processes, and how this governs the turnover of deep soil C pools in peatlands, was the prime objective of the first phase of LTREB funding. Results during that initial LTREB funding period showed that sedge and Equisetum (horsetail) rhizospheres indeed had oxidizing effects on peat and dissolved organic matter. However, persistent flooding over this period of research has presented key gaps in mechanistic understanding of controls on trace gas production in this system, and revealed that plant community structure and the dominance of algae likely have unique controls on soil redox processes and C fluxes. Flooding history also exerted strong control over the relative activity of algae vs. heterotrophic microorganisms, depending on changes in C substrates from different plants. Exactly how changes in plant community interact with altered water tables in governing the supply of electron donors and acceptors, and how this controls anaerobic metabolism in low- and high-water table years, are key questions this collaborative team will examine in the next five years.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.