Methane Metabolism And Functional Microorganisms In Permafrost Soils From The Gas Hydrate Drilling Area Of Qilian Mountains, China

Methane?CH₄?,as an important greenhouse gas in the atmosphere,is an essential factor leading to global climate change.The permafrost region of Qilian Mountains is a vital distribution area of terrestrial gas hydrate in China.CH₄ sources in this region are extensive,including thermogenic gas,biogenic gas,mixed-genetic gas,and hydrate decomposition gas.Among them,methanogenesis by methanogens is an important biological source of atmospheric CH₄.At the same time,methanotrophs play an essential role in controlling the final CH₄ emissions from permafrost.In this paper,the characteristics of methane production and oxidation of microorganisms in this region were investigated by methods of laboratory culture,and the changes in community structure and abundance of methanogens and methanotrophs were analyzed.The conclusions were as follows:1.A 84-days soil methanogenesis experiment was conducted under anaerobic conditions.The effects of temperature and pH on soil methanogensis rate were studied utilizing laboratory simulated warming and setting different pH conditions.There was a positive correlation between soil methanogensis rate and incubation temperature?5²5°C?in this study region.Methanogensis rate in surface soil was higher than that in bottom soil,and methanogensis rate in the natural ecosystem of alpine swamp meadow was higher than that in alpine grassland and alpine meadow.The change of pH?6.5⁷.5?has little effect on the methanogensis rate in surface soil.2.To further explore the pathway of soil CH₄ generation in the study region,seven single carbon sources were added to the culture samples,and a 56-days methanogenesis experiment was conducted at 25°C.CH₄ was mainly produced by aceticlastic and methylotrophic methanogenesis in surface soil,and the primary available substrates were acetate,methanol,and trimethylamine.The primary methanogenesis pathway in the bottom soil was CO₂-reducing methanogenesis,and the primary available substrate was formate.3.A 30-days CH₄ oxidation experiment was conducted under aerobic conditions.The effects of temperature on soil CH₄ oxidation rate were studied utilizing laboratory simulated warming.There was a positive correlation between soil CH₄ oxidation rate and incubation temperature?5²5°C?.The CH₄ oxidation rate in surface soil was higher than that in bottom soil,and the difference of CH₄ oxidation rate between the natural ecosystem of alpine swamp meadow and alpine meadow was small and higher than that in alpine grassland.4.After incubation at 25°C,Methanobacteriales were the dominant methanogenic groups in the surface and bottom soils of alpine grassland,the bottom soils in the natural ecosystem of alpine meadow and alpine swamp meadow,and Methanosarcinales were the dominant methanogenic groups in the surface soils of the natural ecosystem of alpine meadow and alpine swamp meadow.After incubation,the copy number of mcrA gene of methanogens increased 2³0 times.The dominant group of methanotrophs changed from methylobacter to Methylocystis cultured at25°C,and the copy number of pmoA gene of methanotrophs increased 1³ times.5.The CH₄ absorption value(-6.196?mol d^-1 g^-1 soil)in the hydrate region was lower than that in the non-hydrate region(-2.094?mol d^-1 g^-1 soil),indicating that the former has higher CH₄ oxidation activity;the CH₄ release value(0.022?mol d^-1 g^-1soil)in the hydrate region was higher than that in the non-hydrate region(0.004?mol d^-1 g^-1 soil),indicating that the former has higher CH₄ production activity.6.The calculation results in this paper showed that the study area was characterized by weak CH₄ sink,with an average annual CH₄ emissions of about-1.21×10^-3 Tg.