Emissions Of CH₄ And Its Microbial Mechanism In The Permafrost Regions Of The Upper Heihe River Basin

The Qinghai-Tibet Plateau is the largest permafrost area in China.It stores a large amount of soil organic carbon?SOC?.Permafrost soil organic carbon is very sensitive to temperature.Climate warming will induce permafrost degradation,accelerate the decomposition of organic carbon by microorganisms and the release of greenhouse gases.The main greenhouse gases release caused by permafrost degradation are CO2,while CH4 could not be ignored.CH4 emissions are the result of dynamic regulation of methanogens and methanogenic bacteria.Under the climate warming scenarios,studying the CH4 release and microbial mechanisms of the Qinghai-Tibet Plateau permafrost is an important step towards to the assessment of permafrost carbon feedback.This paper studied the soils at different altitudes in the permafrost region of the upper reaches of the Heihe River.The soil samples of 0-15 cm and 15-30 cm were collected,and their physical and chemical variables,such as total carbon?TC?,total nitrogen?TN?,soil organic carbon?SOC?,pH,moisture content that were analyzed at different altitudes.Using real-time fluorescence quantitative?qPCR?technology,this study quantitatively determined the functional gene abundance of methanogens?mcrA?and methanogenic bacteria?pmoA?in the study area;The community structures of methanogens and methanogenic bacteria at the family level in soils at different altitudes in the study area were examined using Illumina MiSeq sequencing technology.The purpose of this study is to clarify the characteristics of methane release and its microbial driving mechanism in soils at different altitudes.The results of the study are helpful for understanding the numbers and structures of methanogens and methanogenic bacteria in permafrost,and to reveal the methane metabolism in permafrost regions.The main conclusions of this study are as follows:?1?The contents of TC,TN,and SOC increase gradually with altitude;At the same altitude,the contents of TC,TN,and SOC in the 0-15 cm layer of soil are all higher than those in the 15-30 cm layer.Soil C and N contents are affected by soil water content.?2?Incubation experiments showed that:1)the methane production rate of soil at the same temperature and different altitudes is different.2)Incubation experiments using the same soil layers at the same temperature at different altitudes,showed that under 0?and10?,the methane production rate showed a decreasing trend with altitude?except for 3900m?.At 5?incubation conditions,the methane production rate fluctuated and there was no obvious change among different elevations.3)Under the incubation conditions of the same soil layer and the same temperature at different altitudes,the methane production rate largely decreased with extension of the incubation time.4)The methane production rate of soil cultivated at the same altitude is different at different temperatures.The methane production rate obtained under the 5?culture condition is slightly higher than that of 0?and 10?.5)The Q10 values of methane emissions from 0-15 cm at different altitudes varied from 0.79to 1.83,and the Q10 values of methane emissions from 15-30 cm layers varied from 0.89 to1.28.The Q₁₀0 value of this study confirmed that the methane production is sensitive to temperature.The release of soil methane in the permafrost region in the upper reaches of the Heihe River is sensitive to temperature changes,and increasing temperature promotes the production and release of methane.?3?The copy number of mcrA functional genes of methanogens in soil layers at different depths decreased with altitude.The functional gene abundance of methanogens is closely related to TN and SOC,and the functional gene abundance of methanogenic bacteria is significantly negatively related to TC and soil moisture content?P<0.05?.This result showed that soil TN and SOC affected the relative abundance of methanogens,while TC and soil moisture content affected the relative abundance of methanogenic bacteria.?4?The dominant families of methanogens at different altitudes were Methanoregulaceae,Methanosaetaceae,Methanomassiliicoccaceae,Methanocellaceae,Methanobacteriaceae,Methanomicrobiaceae.Among them,Methanoregulaceae was a dominant family of fungi at all altitudes,and its abundance varies from 8.7%to 32.4%.The methanogens in the study area were mainly hydrogen-trophic methanogens?the relative abundance was 52.5%?and methyl-trophic methanogens?the relative abundance was 11.4%?.The dominant families of methanogenic bacteria were Methylococcaceae and Beijerinckiaceae.Among them,the relative abundances of Methylococcaceae were higher than 68.9%at all altitudes.The methanogenic bacteria in the study area were Type I methanogenic bacteria,whose total relative abundance was higher than 88%.?5?There was a significant positive relationship between soil moisture content and nutrients and methanogens community diversities?Simpson,Shannon index?and community richness?Chao 1,Ace index??P<0.05?.There was a significant negative relationship between substrate and community diversities?Simpson,Shannon index?and community richness?Chao 1,Ace index?of methanogenic bacteria?P<0.05?.The physical and chemical properties of soil affected the richness and distribution of methanogens and methanogenic bacteria.?6?RDA analysis of environmental factors and methanogens and methanogenic bacteria showed that Methanoregulaceae,Methanomicrobiaceae,Methanomassiliicoccaceae,Methanocellaceae,Methanobacteriaceae were correlated with soil moisture content,pH in different 0-15 cm,15-30 cm soil layers.There was a significant relationship?P<0.05?between Methanoregulaceae,Methanomicrobiaceae,and Methanomassiliicoccaceae and soil nutrients in the 0-15 cm soils.The Methanoregulaceae,Methanomicrobiaceae,Methanocellaceae,Methananosaceae,Methanobacteriaceae and Methanobacteriaceae significantly correlated with soil nutrients in the 15-30 cm soils?P<0.05?.Methylococcaceae was positively correlated with soil moisture content and pH in 0-15 cm and 15-30 cm layers.Beijerinckiaceae was positively correlated with 0-15 cm soil moisture content,SOC,pH and15-30 cm soil SOC?P<0.05?,but it was negatively correlated with 15-30 cm soil water content,pH?P<0.05?.Soil water content,pH,and nutrient substrates were important influencing factors affecting the community structures of methanogens and methanogenic bacteria.The results of this study indicate that temperature increase in the study area will promote methane release.The methane-metabolizing microorganisms in the permafrost region of the upper Heihe River are mainly hydrogen trophic methanogens and Type?aerobic methanogenic bacteria.The factors affecting methanogens and methanogenic bacteria in the same soil layer are different,and the factors affecting the structure of methane functional microorganism community are different in different soil layers.The relationships between methanogens and methanogenic bacteria and environmental factors are complex,which can be explained as the combining effects of multiple environmental factors.