Activation of methanogenesis in arid biological soil crusts despite the presence of oxygen.
Activation of methanogenesis in arid biological soil crusts despite the presence of oxygen.
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DOI：
10.1371/journal.pone.0020453
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发表时间：
2011
期刊：
影响因子：
3.7
通讯作者：
Conrad R
中科院分区：
文献类型：
--
作者：
Angel R;Matthies D;Conrad R
传统上认为，产甲烷只发生在高度还原的缺氧环境中。湿地和稻田土壤是众所周知的大气甲烷的来源，而曝气土壤被认为是汇。虽然在一些曝气土壤甚至沙漠土壤中检测到少量产甲烷菌，但它们在自然氧化条件下是否有活性尚不清楚，例如在干旱地区的生物土壤结皮（BSCs）中。为了回答这个问题，我们在模拟自然条件下使用微观世界进行了析因实验。在干旱土壤上的BSC在潮湿条件下孵育，在所有可能的洪水和排水组合，光和暗，空气和氮顶空。在光线下，氧气是通过光合作用产生的。在所有微观环境中都检测到甲烷的产生，但当氧气存在时，甲烷的产生率要低得多。此外，甲烷的δ13C在富氧/富氧和缺氧微观环境中存在差异。在缺氧条件下，甲烷主要由乙酸酯生成，而在富氧条件下，甲烷几乎完全由H2/CO2生成。在BSC-Methanosarcina和Methanocella中仅鉴定出2个产甲烷菌属；它们在缺氧条件下转录mca基因（编码甲基com还原酶）的丰度和活性分别高于缺氧/富氧条件。两种产甲烷菌也积极转录除氧基因过氧化氢酶。由于BSC中没有检测到甲烷氧化菌，因此产生的所有甲烷都被释放到大气中。我们的发现指出，沙漠土壤参与了全球甲烷循环，这在以前是未知的。
Methanogenesis is traditionally thought to occur only in highly reduced, anoxic environments. Wetland and rice field soils are well known sources for atmospheric methane, while aerated soils are considered sinks. Although methanogens have been detected in low numbers in some aerated, and even in desert soils, it remains unclear whether they are active under natural oxic conditions, such as in biological soil crusts (BSCs) of arid regions. To answer this question we carried out a factorial experiment using microcosms under simulated natural conditions. The BSC on top of an arid soil was incubated under moist conditions in all possible combinations of flooding and drainage, light and dark, air and nitrogen headspace. In the light, oxygen was produced by photosynthesis. Methane production was detected in all microcosms, but rates were much lower when oxygen was present. In addition, the δ13C of the methane differed between the oxic/oxygenic and anoxic microcosms. While under anoxic conditions methane was mainly produced from acetate, it was almost entirely produced from H2/CO2 under oxic/oxygenic conditions. Only two genera of methanogens were identified in the BSC-Methanosarcina and Methanocella; their abundance and activity in transcribing the mcrA gene (coding for methyl-CoM reductase) was higher under anoxic than oxic/oxygenic conditions, respectively. Both methanogens also actively transcribed the oxygen detoxifying gene catalase. Since methanotrophs were not detectable in the BSC, all the methane produced was released into the atmosphere. Our findings point to a formerly unknown participation of desert soils in the global methane cycle.
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