| Since the end of the Little Ice Age(around 1858),climate warming has led to the melting of glacier.The region exposed by the retreat of glaciers is called the glacial foreland.Currently,they are an important field of ecological succession.The climate change in the Arctic is much faster than that of the entire earth.This phenomenon is called the Arctic Amplification.In different ecosystems around the world,peatlands and permafrost are of great concern,because if climate change leads to conditions unfavorable for the accumulation or preservation of organic matter,a large amount of carbon may be released into the atmosphere and cause serious greenhouse effect.The runoff formed by melting glaciers into the ocean may also have an impact on sea level rise and the structure of marine microbial communities.The purpose of this study is to understand the succession of microbial community structure and function in the Arctic glacier foreland,and obtain a large number of microbial resources and potential new taxa from the Arctic.The Austre Lovenbreen Glacier(A Glacier)is located in the Svalbard in the Arctic,Norway.The average annual glacier retreat rate from 1948 to 2013 was 16.7 ± 0.3m.The soil samples of this study were collected from quadrots on the forelands of the A Glacier in September 2017.The quadrots were located at the location of the A glacier terminus in 1990(D6)and 1936(D7),and at the end of the Little Ice Age(D8),and areas not covered by glaciers for more than two thousand years(D9).In this study,the microbial biomass and microbial community composition in the soil of the four quadrots of the A Glacier foreland were analyzed by phospholipid fatty acid(PLFA)method and High-throughput sequencing.Along the chronosequence,the microbial biomass,as indicated by PLFA,were found to increase significantly.Whether PLFA or High-throughput sequencing,showed that there is a significant difference in the microbial community structure between each sample.Based on the study of PLFA,it was found that bacteria were the dominant group,followed by fungi;Gram-positive bacteria and actinomycetes were not detected in D6 and increased sequentially in D7,D8,and D9;the relative abundance of symbiotic fungi in D7 was the highest.The rRNA gene sequencing and metagenome sequencing were used to detect and analyze the microbial community structure in the glacier foreland.The results showed that the dominant bacterial phyla of the foreland of A glacier are Proteobacteria,Acidobacteria,Cyanobacteria,Actinobacteria,Bacteroidetes;The dominant fungi phyla are Ascomycota,Basidiomycota,and Zygomycota;The dominant archaea phyla are the Euryarchaeota and Thaumarchaeota.In addition,the Proteobacteria,Cyanobacteria,and Bacteroidetes were the main groups in the early stage of succession,while the Proteobacteria,Acidobacteria,and Actinobacteria are the main groups in the late stage;Ascomycete and Zygomycota(or Glomeromycota)are dominant fungi phyla in the early stage of succession,while Ascomycete and Basidiomycete as the main groups in the late stage;Euryarchaeota are the dominant archaea in the early succession,whlie Euryarchaeota and Thaumarchaeota as the main group in the late succession stage.The results of rRNA gene sequencing and metagenomic sequencing are roughly the same,but there are also differences.This may be due to the amplification strategy in rRNA gene sequencing,the metagenome database does not provide a comprehensive annotation of functional gene,and the genes copy number and other reasons.The hierarchical clustering heatmap analysis and principal component analysis showed that the soil elements and environmental factors of the four samples were significantly different.The dbRDA and Monte Carlo substitution tests(999 substitutions)revealed that the bacterial community structure was significantly affected by Si,P,water content and plant coverage.The fungal community structure is mainly affected by Si,P,Cr,water content and plant coverage.The archaeal community structure is mainly affected by Si,P,K,TC,NO3--N and pH.Analysis of differences in genetic potential for carbon,nitrogen and sulfur cycling processes revealed that the most important processes in the carbon cycle are aerobic respiration(38.72%)and carbon monoxide oxidation(33.02%).It is speculated that microbes in the glacier foreland obtains energy mainly through aerobic respiration,and simultaneously it oxidizes carbon monoxide in the air to obtain energy.The most important process in the nitrogen cycle is nitrogen assimilation(53.12%),followed by nitrogen mineralization(25.98%),indicating that the source of nitrogen in the soil of the A Glacier foreland is mainly from nitrogen mineralization.The most abundant processes in the sulfur cycle are sulfur mineralization(63.60%)and assimilation sulfate reduction(38.26%).Organic sulfur mineralization is an important sulfate supply process in the soil,which has an important role.The carbon,nitrogen and sulfur cycle processes have some shifts in each sample:in the early stage it may more rely on aerobic carbon fixation and nitrogen assimilation to obtain carbon and nitrogen sources,and aerobic respiration and fermentation to obtain energy,and it shows a downward trend with succession.The process of reduction of nitrate to ammonium and the process of CO oxidation increase with succession,and gradually provide nitrogen and carbon sources for the ecological environment.The mature soil that is not covered by glaciers is obviously different from the soil that is covered by glaciers in the process of succession,its anaerobic carbon fixation,DNRA and polysulfide reduction processes are less abundant.Finally,a study of culturable bacteria was carried out on three sediment samples collected from Kongsfjorden,Arctic,in 2017.A total of 157 strains were isolated,belonged to 4 phyla,which were Proteobacteria(51.6%),Bacteroidetes(26.1%),Actinobacteria(21.0%),and Firmicutes(1.3%).Polyphasic taxonomic approach was used to identify a potential novel bacteria.Based on phylogenetic,physiological and chemotaxonomic data,the novel species was proposed,and named according to the isolation of the strain,it was designated as a new species of genus Roseovarius:Roseovarius arcticus MK6-18T(=CCTCC AB 2018219T=KCTC 72187T).Until now,the research results of strain MK6-18T have been published. |
