Can iron-metabolizing bacteria control the fate of carbon during permafrost thaw?

高纬度永久冻土泥炭地储存了地球土壤碳储量的14%左右，尽管它们只覆盖了地球表面的3%左右。这些巨大的有机碳储量使得高纬度泥炭地对气候反馈机制有着不成比例的重要性，特别是考虑到北半球正在经历高于平均水平的变暖速度。人们非常担心，永久冻土解冻可能会释放储存的有机碳，并使其以二氧化碳和甲烷的形式排放出去，从而可能进一步加剧气候变暖。此外，与永久冻土融化相关的水文变化最终导致土壤淹水，从而观测到大量甲烷排放。我们和其他人已经观察到，活性土壤矿物质可能在完整永久冻土层的碳稳定中起关键作用，正如在许多不同的土壤和沉积物环境中观察到的那样。事实上，在我们之前的工作中，我们已经表明，在我们的模型现场，瑞典永久冻土泥炭地的某些土壤层中，高达20%的碳可能与活性的、结晶性差的铁（III）（氧合）氧化物结合在一起。然而，由于微生物矿物的减少，这种“生锈的碳汇”在永久冻土融化期间迅速失稳。这提出了许多悬而未决的问题，如永久冻土融化过程中铁和碳循环的动态变化，以及铁矿形成和溶解对碳固存和温室气体排放的影响，我们将在本提案中解决这些问题。具体来说，在第一步，我们将确定在不同解冻阶段与铁矿物相关的碳（有机化合物）的数量、特性、质量和生物利用度，我们将识别、量化和分离参与碳结合铁矿物形成和破坏的铁（II）氧化和铁（III）还原微生物。在第二步中，我们将量化铁矿物的形成和破坏以及碳释放和生物利用度的增加对温室气体排放（CO2和CH4）的影响程度。

High latitude permafrost peatlands store around 14% of Earth’s soil carbon stocks despite covering only around 3% of the land surface. These large organic carbon stores make high latitude peatlands disproportionately important for climate feedback mechanisms, especially considering that the northern hemisphere is experiencing above average rates of warming. There is much concern that permafrost thaw may release stored organic carbon and allow it to be emitted as CO2 and CH4, potentially further exacerbating climate warming. Additionally, hydrological changes associated with permafrost thaw eventually lead to waterlogged soils under which high methane emissions are observed. It has been observed by us and others, that reactive soil minerals may play a key role in carbon stabilization in intact permafrost as is observed across many different soil and sediment environments. Indeed, in our previous work we have shown that up to 20% of carbon in certain soil horizons in our model field site, a Swedish permafrost peatland, could be bound to reactive, poorly crystalline Fe(III) (oxyhydr)oxides. However, this “rusty carbon sink” is rapidly de-stabilized during permafrost thaw due to microbial mineral reduction. This raises many unanswered questions regarding how the dynamics of Fe and C cycling change during permafrost thaw, and the effect of iron mineral formation and dissolution on carbon sequestration and greenhouse gas emissions which we will address in this proposal. Specifically, in a first step we will determine the amount, identity, quality and bioavailability of carbon (organic compounds) associated with iron minerals at different thaw stages and we will identify, quantify and isolate the iron(II)-oxidizing and Fe(III)-reducing microorganisms involved in formation and destruction of carbon-binding iron minerals. In a second step we will then quantify the extent to which formation and destruction of iron minerals, and thus carbon release and increased bioavailability, influences greenhouse gas emissions (CO2 and CH4).