Collaborative Research: Long-term changes in peatland C fluxes and the interactive roles of soil climate, vegetation, and redox supply in governing anaerobic microbial activity

北部泥炭地储存了世界土壤碳的很大一部分（30%），鉴于它们在高纬度地区的优势，预计将以全球两倍的速度变暖。因此，如果泥炭地变暖导致分解速度加快，导致这些碳释放到大气中，就很有可能对全球气候产生强烈的反馈。我们目前对泥炭地碳循环的看法表明，大部分分解发生在地下水位以上的薄而富氧的泥炭层。一旦碳被转移到更深的饱和泥炭层，由于低温和低氧条件抑制了分解，碳的分解率被认为可以忽略不计。然而，地下水位以下的泥炭土碳可以被微生物利用各种不依赖于自由氧的生化过程分解，但能量效率较低。这些替代的代谢途径可导致甲烷（CH4）的产生，甲烷是一种比二氧化碳（CO2）具有更高温室增温潜力的微量气体。因此，地下水位的位置传统上被用作泥炭地总体分解率和甲烷产量的预测指标。然而，阿拉斯加泥炭地地下水位操纵实验（阿拉斯加泥炭地实验，简称APEX）的初步结果表明，深层泥炭层的分解和由此产生的二氧化碳产量可能比之前认为的要高。这项研究的目标是调查深层泥炭层碳分解的驱动因素，并利用这些信息通过改进泥炭地对全球气候影响的未来预测来造福社会。这项研究还将为本科生和研究生的培训提供宝贵的机会，并通过与校园LTER项目的合作，教育学童了解气候变化的驱动因素和影响。在过去的8年里，APEX研究通过监测土壤湿度和温度、植物组成和生物量以及生态系统CO2和CH4通量的变化，研究了土壤气候和植被变化对泥炭地碳循环的影响。该实验包括一个因子设计的地下水位处理（包括降低地下水位模拟干燥，提高地下水位模拟洪水）和表面土壤变暖的阿拉斯加沼泽。这项研究揭示了我们对泥炭地微生物分解过程的理解差距，并为本项目中正在测试的假设提供了背景。特别是，先前的研究表明，不同的植物功能类型在决定好氧和厌氧泥炭分解过程中与地下水位相互作用。此外，植物功能类型之间凋落物化学的变化被假设为泥炭地分解速率的主要驱动因素。总的来说，这些因素表明，植被的变化对泥炭地的厌氧分解过程起着重要的控制作用，但迄今为止，这些影响还没有得到充分的研究，部分原因是在方法上难以将植被与对分解的水文控制分开。在这个项目中进行的新实验旨在提供对一系列因素的机械见解，包括植被的作用，控制泥炭地碳的稳定。

Northern peatlands store a large proportion (30%) of the world's soil carbon, and given their predominance at high latitudes are expected to experience warming at twice the global rate. Warming of peatlands, therefore, has high potential to create strong feedbacks to global climate if it causes accelerated rates of decomposition that result in the release of this carbon to the atmosphere. Our current view of carbon cycling in peatlands suggests that the majority of decomposition occurs in the thin, oxygen-rich peat layer above the water table. Once carbon is transferred to deeper, saturated peat layers, decomposition rates of carbon are thought to be negligible due to cold temperatures and low-oxygen conditions that inhibit decomposition. Peat soil carbon below the water table can, however, be decomposed by microbes using a variety of biochemical processes that don't rely on free oxygen, but are energetically less efficient. These alternative metabolic pathways can result in the production of methane (CH4), a trace gas with much higher greenhouse warming potential than carbon dioxide (CO2). Thus, the position of the water table has traditionally been used as a predictor of overall decomposition rates and methane production in peatlands. However, preliminary results from an Alaskan peatland water-table manipulation experiment (the Alaska Peatland Experiment, or APEX) suggest that decomposition and resulting CO2 production may be higher in deeper peat layers than previously thought. The goals of this research are to investigate the factors driving decomposition of carbon in deep peat layers, and to use this information to benefit society by improving future projections of the impact of peatlands on global climate. This study will also provide valuable opportunities for the training of undergraduate and graduate students, and to educate school children on the drivers and impacts of climate change through collaboration with the Schoolyard LTER program. Over the past 8 years, research on APEX has examined the role of changing soil climate and vegetation on peatland carbon cycling through monitoring changes in soil moisture and temperature, plant composition and biomass, and ecosystem CO2 and CH4 fluxes. The experiment includes a factorial design of water table treatments (including lowering the water table to simulate drying, and raising the water table to simulate flooding) and surface soil warming in an Alaskan fen. This research has revealed gaps in our understanding of microbial decomposition processes in peatlands, and provides the context for the hypotheses being tested in this project. In particular, previous work suggests different plant functional types interact with water table in determining aerobic and anaerobic peat decomposition. In addition, variation in litter chemistry between plant functional types is hypothesized to be a major driver of decomposition rates in peatlands. Collectively, these factors suggest that changes in vegetation exert significant control over anaerobic decomposition processes in peatlands, but to date these effects have not been studied adequately, in part because it is difficult methodologically to separate vegetation from hydrologic controls on decomposition. New experiments being conducted in this project are designed to provide mechanistic insights into a suite of factors, including the role of vegetation, that control stabilization of peatland carbon.