Biosciences Division, Oak Ridge National Laboratory, Oak Ridge, TN, United States of America.
Climate Change Sciences Institute, Oak Ridge National Laboratory, Oak Ridge, TN, United States of America.
PLoS One. 2020 Feb 6;15(2):e0223744. doi: 10.1371/journal.pone.0223744. eCollection 2020.
Peatlands play outsized roles in the global carbon cycle. Despite occupying a rather small fraction of the terrestrial biosphere (~3%), these ecosystems account for roughly one third of the global soil carbon pool. This carbon is largely comprised of undecomposed deposits of plant material (peat) that may be meters thick. The fate of this deep carbon stockpile with ongoing and future climate change is thus of great interest and has large potential to induce positive feedback to climate warming. Recent in situ warming of an ombrotrophic peatland indicated that the deep peat microbial communities and decomposition rates were resistant to elevated temperatures. In this experiment, we sought to understand how nutrient and pH limitations may interact with temperature to limit microbial activity and community composition. Anaerobic microcosms of peat collected from 1.5 to 2 meters in depth were incubated at 6°C and 15°C with elevated pH, nitrogen (NH4Cl), and/or phosphorus (KH2PO4) in a full factorial design. The production of CO2 and CH4 was significantly greater in microcosms incubated at 15°C, although the structure of the microbial community did not differ between the two temperatures. Increasing the pH from ~3.5 to ~5.5 altered microbial community structure, however increases in CH4 production were non-significant. Contrary to expectations, N and P additions did not increase CO2 and CH4 production, indicating that nutrient availability was not a primary constraint in microbial decomposition of deep peat. Our findings indicate that temperature is a key factor limiting the decomposition of deep peat, however other factors such as the availability of O2 or alternative electron donors and high concentrations of phenolic compounds, may also exert constraints. Continued experimental peat warming studies will be necessary to assess if the deep peat carbon bank is susceptible to increased temperatures over the longer time scales.
泥炭地在全球碳循环中起着重要作用。尽管它们仅占陆地生物群系的一小部分（约 3%），但这些生态系统却占据了全球土壤碳库的约三分之一。这些碳主要由未分解的植物物质（泥炭）组成，其厚度可达数米。因此，这些深层碳储量在当前和未来气候变化下的命运引起了人们的极大兴趣，并有可能对气候变暖产生积极反馈。最近对一个寡营养泥炭地的原位增温表明，深层泥炭微生物群落和分解速率对高温具有抗性。在这项实验中，我们试图了解养分和 pH 值限制如何与温度相互作用，从而限制微生物活性和群落组成。从 1.5 到 2 米深采集的泥炭厌氧微宇宙在 6°C 和 15°C 下，用升高的 pH 值、氮（NH4Cl）和/或磷（KH2PO4）在完全因子设计中进行培养。尽管在两个温度下微生物群落结构没有差异，但在 15°C 下培养的微宇宙中 CO2 和 CH4 的产生明显更大。将 pH 值从约 3.5 升高到约 5.5 会改变微生物群落结构，但 CH4 产生的增加并不显著。出乎意料的是，N 和 P 的添加并没有增加 CO2 和 CH4 的产生，这表明在深层泥炭的微生物分解中，养分供应不是主要限制因素。我们的研究结果表明，温度是限制深层泥炭分解的关键因素，但其他因素，如 O2 的可用性或替代电子供体和高浓度的酚类化合物，也可能施加限制。需要进行持续的实验性泥炭增温研究，以评估在更长时间尺度上深层泥炭碳库是否容易受到温度升高的影响。
