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

北部(北方)泥炭地全球重要的碳(C)储存很容易受到降水和径流模式变化、地下水输入以及高纬度冻土(称为永久冻土或冰冻圈)范围变化的影响。这些变化可能会影响北方湿地的范围，以及它们隔离和转化碳和其他养分的能力。2005年，创建了阿拉斯加泥炭地实验(APEX)，以研究土壤气候和植被变化对泥炭地C循环的作用。在过去的15年里，收集了关于土壤水分和温度、植物成分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，无论地下水位处于什么位置，该试验场的碳排放量似乎都很高，这表明，植物物种组成对处理的响应变化之间的相互作用强烈地控制着该生态系统保持碳的能力。这是长期环境生物学研究项目DEB-1354370的五年续展。这项研究正在研究水文变化、植物种类组成变化和气候变化(特别是洪涝和干旱)之间的相互作用，以控制这一泥炭地复合体中的碳储存；这项工作对于了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员都将接受现场和实验室技术方面的培训。这项研究的结果还将被纳入新的高中课程，用于培养科学夏令营。目前关于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充气泥炭层(顶端)，而出现在缺氧层(泥炭层)中的深层泥炭碳经历了最小的分解。因此，地下水位的位置(以及与之相关的顶端厚度)被用作总体分解速率和长期泥炭堆积率的预测因子。然而，这个团队在阿拉斯加沼泽(阿拉斯加泥炭地实验，APEX)中对地下水位位置进行了长达15年的操纵，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快于之前的预期，导致了高通量的厌氧二氧化碳产生。以前的分析表明，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是由于在较低(较干)和较高(较湿)地下水位位置下发生的植被变化。最初的实验设计无法理清水文植被变化对泥炭氧化还原和碳通量的影响。因此，了解水文和植被变化对厌氧分解过程的相互影响，以及这如何管理泥炭地深层土壤碳库的周转，是LTREB第一阶段资金的主要目标。在LTREB最初资助期间的结果表明，莎草和木贼(马尾)根际确实对泥炭和溶解有机物有氧化作用。然而，在这段时间里，持续的洪涝灾害在控制该系统中微量气体产生的机制方面存在关键差距，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。淹水历史也对藻类与异养微生物的相对活性施加了强有力的控制，这取决于不同植物的C底物的变化。植物群落的变化如何与改变的地下水位相互作用来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，是这个合作团队在未来五年将研究的关键问题。这一奖项反映了NSF的法定使命，并通过使用基金会的智力优势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.