Study On Soil Microbial Community Structure And Enzyme Activity Of Swamp In The Greater Khingan Mountain Permafrost Region

The degradation of permafrost caused by global warming will significantly change the hydrological process and soil carbon pool stability of wetlands in cold regions.Soil microbial communities and extracellular enzyme activities are crucial for maintaining functional stability of wetland ecosystems in cold regions.In this study,the Nanwenghe National Nature Reserve in the permafrost region of the Greater Khingan Mountain was selected as the research area.Five representative fixed experimental plots were set up along a moisture gradient running from forest to swamp and according to water table and vegetation type,including Larix gmelinii swamp,Betula platyphylla swamp,Alnus sibirica var.hirsute swamp,thicket swamp and tussock swamp.High-throughput sequencing technology and microplate fluorescence method were used to analyze the structure and diversity of soil bacterial and fungal communities,to clarify the spatial variability of soil extracellular enzyme activity and its stoichiometric ratio,identify the relationship among microorganisms,extracellular enzymes,and soil environmental factors.Providing theoretical basis for revealing the response mechanism of wetland ecosystems in permafrost regions to climate change.（1）Both the Observed＿species and Chao1 indices showed Betula platyphylla swamp>thicket swamp>Larix gmelinii swamp>Alnus sibirica var.hirsute swamp>tussock swamp in soil bacterial community.The Principal component analysis（PCA）results showed that there was a significant difference between Larix gmelinii swamp and Betula platyphylla swamp,while Alnus sibirica var.hirsute swamp,thicket swamp,and tussock swamp were similar in soil bacterial community structure.The dominant bacteria were Proteobacteria（19.3%-44.6%）,Acidobacteriota（10.1%-31.8%）,Actinomycetota（14.3%-32.2%）,Verrucomicrobiota（2.4%-12.6%）,and Chloroflexota（5.6%-6.5%）.Along the direction from forest to swamp,the relative abundance of Proteobacteria showed an upward trend,while Actinomycetota showed a downward trend;the relative abundance of Acidobacterota was relatively high in Betula platyphylla swamp and Alnus sibirica var.hirsute swamp;the relative abundance of Verrucomicrobiota in thicket swamp and tussock swamp was significantly higher than others（P<0.05）;the relative abundance of Chloroflexota was no significant difference among different swamps（P>0.05）.（2）Observed＿species,Chao1,and Shannon indices of soil fungal community were higher in Larix gmelinii swamp and Betula platyphylla swamp,but lower in tussock swamps.PCA results showed that Larix gmelinii swamp and Betula platyphylla swamp were similar in soil fungal community structure.At the phylum level,the dominant fungi were Ascomycota and Basidiomycota,and the relative abundance of Ascomycota in all soil samples is above 66%,accounting for an absolute advantage.The relative abundance of Ascomycota in thicket swamp and tussock swamp was significantly higher than other swamps;the relative abundance of Basidiomycota was significantly lower in thicket swamp and tussock swamp than others,with the highest in Betula platyphylla swamp at 10-20 cm（22.83%）and the lowest in tussock swamp at 10-20 cm（0.77%）.（3）The activity ofβ-glucosidase（BG）andβ-N-acetylglucosaminidase（NAG）in thicket swamp and tussock swamp was significantly lower than other swamps,manifested as Alnus sibirica var.hirsute swamp>Larix gmelinii swamp>Betula platyphylla swamp>thicket swamp>tussock swamp;the activity of leucine aminopeptidase（LAP）was highest in thicket swamp at 0-10 cm;the activity of acid phosphatase（AP）in Betula platyphylla swamp was significantly higher than other swamps（P<0.05）;however,the activity of cellobiohydrolase（CB）was no significant difference among different swamps（P>0.05）.The activities of BG,NAG,and AP in Larix gmelinii swamp and Betula platyphylla swamp differed significantly between0-10 cm and 10-20 cm（P<0.05）.The results of extracellular enzymatic stoichiometry showed that the value range of（BG+CB）:（NAG+LAP）was 1.27-1.76;the value range of（BG+CB）:AP and（NAG+LAP）:AP was 0.49-0.81 and 0.32-0.63.（4）Along the direction from forest to swamp,soil water content（SWC）and soil ammonium nitrogen（NH₄⁺-N）content showed an upward trend,and the content of total organic carbon（TOC）was significantly higher in thicket swamp and tussock swamp than others（P<0.05）.Pearson analysis showed that the diversity index of bacteria and fungi had a significant correlation with total phosphorus（TP）,nitrate nitrogen（NO₃^--N）,NH₄⁺-N,and pH.BG and LAP showed significant positive correlations with TOC;NAG showed significant negative correlations with NO₃^--N;AP showed significant negative correlations with TP（P<0.05）.Redundancy analysis（RDA）of soil environmental factors and microbial communities showed that SWC,TOC,and TP were the major contributors to the observed variations in microbial community composition.