Microbial methane cycling in the bed of a chalk river: oxidation has the potential to match methanogenesis enhanced by warming
Microbial methane cycling in the bed of a chalk river: oxidation has the potential to match methanogenesis enhanced by warming
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DOI：
10.1111/fwb.12480
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发表时间：
2015-01-01
影响因子：
2.7
通讯作者：
Trimmer, Mark
中科院分区：
文献类型：
--
作者：
Shelley, Felicity;Abdullahi, Frah;Trimmer, Mark
相对于大气，许多河流的甲烷（CH4）和二氧化碳（CO2）含量过高，但我们对这两种重要温室气体之间平衡的生物控制以及它们对气候变暖的反应知之甚少。在对比的河床沉积物中，我们描述了CO2和CH4的生物生产和随后的CH4微生物氧化对温度的潜在响应，这是CH4循环的汇和源成分：细沉积物（主要是缺氧的）和含氧的粗砾石。细粒沉积物中CH4和CO2厌氧产气量均随温度升高而增加，其表观活化能分别为0.51 eV和0.24 eV。两者之间的差异导致温度每升高1摄氏度，CH4:CO2产量的比例就会增加4%。在粗砾石中，由于底物的强烈限制，在这些砾石层特征的CH4浓度（30-200nmol CH4L-1）下，微生物的CH4氧化对温度没有响应。相比之下，在较高的CH4浓度（尽管仍有速率限制）下，更具有细沉积物斑块特征（2-4mol CH4L-1）， CH4氧化对温度的响应越来越强，最终超过了CH4生成的响应。在细粒沉积物中，表层的CH4氧化能力是砾石的100倍以上，不同孔隙水CH4浓度的动力学响应意味着，细粒沉积物斑块中CH4的氧化速度比粗粒沉积物快2000倍左右。计算的动力学响应和温度响应表明，随着气候变暖，甲烷生成不太可能超过甲烷化，CO2与CH4的排放比例可以保持不变。因此，CH4 / CO2外排比的任何变化都不太可能是由于甲烷化生物对CH4的产生没有反应，而是由于甲烷化生物群落的物理旁路（例如通过沸腾或通过植物茎的运输）或氧层的收缩。
Many rivers are oversaturated in methane (CH4) and carbon dioxide (CO2) relative to the atmosphere, but we know little about the biological controls on the balance between these two important greenhouse gases and how they might respond to warming.We characterise the potential response to temperature in the biological production of CO2 and CH4 and the subsequent microbial oxidation of that CH4, that is the sink and source components of the CH4 cycle, in contrasting river bed sediments: fine sediments, which are largely anoxic, and oxic, coarse gravels.In the fine sediments, anaerobic production of both CH4 and CO2 increased with temperature, with apparent activation energies for each being 0.51 eV and 0.24 eV, respectively. The difference between the two resulted in a 4% increase in the ratio of CH4:CO2 production for a 1 degrees C increase in temperature.In the coarse gravels, microbial CH4 oxidation showed no response to temperature at CH4 concentrations characteristic of these gravel beds (30-200nmol CH4L-1), due to strong substrate limitation. In contrast, at higher (although still rate limiting) CH4 concentrations, more characteristic of the fine sediment patches (2-4mol CH4L-1), CH4 oxidation exhibited an increasingly strong response to temperature, eventually exceeding that for CH4 production.In the fine sediment, the surface layers had a CH4 oxidation capacity over 100 times greater than the gravels and the kinetic response to differing pore water CH4 concentrations meant CH4 was oxidised some 2000 times faster in the fine sediment patches compared with the coarse gravels.The calculated kinetic and temperature responses showed that with warming, methanogenesis is unlikely to outstrip methanotrophy and the ratio of CO2 to CH4 emitted could be conserved. Consequently, any changes in the efflux ratio of CH4 to CO2 are unlikely to be due to the incapacity of methanotrophy to respond to CH4 production, but rather to a physical bypassing of the methanotrophic community (e.g. through ebullition or transport via plant stems) or contraction of the oxic layer.