Structural Changes And Functional Characteristics Of Soil Microbial Communities During The Decay Of Salix Psammophila Sand Barriers

Salix psammophila sand barrier is a widely used mechanical sand barricade in the desert sand control technology,which mainly plays the role of wind control and sand fixation and promotes vegetation restoration.With the increase of time,the decay and decomposition of sand barriers sand buried part directly affect the effectiveness of soil resources,microbial community structure and function,which are crucial to the nutrient cycling,communitylevel microbial elemental homeostasis and microbial ecological functions of desert ecosystems.In this study,we used in situ field sampling,indoor index determination,chloroform fumigation and high-throughput sequencing techniques to determine soil microbial biomass carbon,nitrogen and phosphorus content and the composition and diversity of soil fungi and bacteria in an S.psammophila sand barriers laid for up to 9 years.This will provide further insight into soil microbial biomass stoichiometry and homeostasis.The main drivers affecting soil microbial C:N:P stoichiometry,community composition and diversity were explored in relation to sand barrier decay properties,basic soil properties and extracellular enzyme activity.On this basis,macro-genome sequencing technology was used to identify the metabolic pathways,enzymes and KOs affecting gene functions,and finally reveal the structural change characteristics and ecological functions of soil microbial communities during the decay of S.psammophila sand barriers.The main conclusions of our investigations are as follows:(1)The mass loss rate increased significantly and the main chemical composition decreased significantly during the decay process of S.psammophila sand barrier.Soil organic carbon and total phosphorus at 7 years increased significantly by 87.07% and 30.77%,respectively(P < 0.05),compared to 1 year,but soil urease and sucrase activities showed a decreasing trend.The C and N content of soil microbial biomass continued to increase with increasing decay,with 7 years being an important temporal turning point.Soil microbial C/N,C/P and N/P at 9 years were significantly higher by 45.35%,277.10% and 160.49%,respectively,compared to 1 year.The continuous increase of soil microbial C:N:P stoichiometric ratio was directly caused by the increase of mass loss and the change of fungal diversity.The C/N and N/P ratios of microorganisms were well constrained over time,indicating that microorganisms had homeostasis,but C/P was not strictly homeostasis at the community level.The higher microbial C/P and N/P ratios indicated that microorganisms were limited by phosphorus after 5 years of sand barrier decay,which was mainly related to the decrease of soil alkaline phosphatase activity.(2)A total of 993 OTUs species were recorded in 11 phyla,29 classes,79 orders,159 families,305 genera,459 species.The dominant species were Ascomycota,Basidiomycota and Mortierellomycota.With the increase of decay years,the abundance of Ascomycota decreased,Basidiomycota increased first and then decreased,and the whole of Mortierellomycota increased.Soil fungal diversity tended to decrease and then increase,and community richness tended to increase and then decrease and then increase.In the first 5years of sand barrier decay,the species composition of fungi was similar,but in the 7 and 9years,the species was different.Eurotiomycetes was significantly negatively correlated with total phosphorus,available phosphorus and pH,but only positively correlated with alkaline phosphatase.The Sordariomycetes were negatively correlated with mass loss,organic carbon,total nitrogen and water content(P < 0.05).The results of RDA analysis showed that mass loss rate and available phosphorus were the driving factors that significantly affected soil fungal dominant community,while urease and pH were environmental factors that significantly affected soil fungal diversity.(3)A total of 4423 species of OTUs were recorded from 36 phyla,104 classes,256 orders,426 families,820 genera,1595 species,among which Proteobacteria,Actinobacteriota and Acidobacteriota were the dominant bacteria groups.With the increase of decay years,Proteobacteria abundance showed a downward trend,Actinobacteriota as a whole showed a downward trend and then an upward trend,while Acidobacteriota showed an upward trend and then a downward trend.The number of soil bacterial species showed an increasing trend and then a gentle decreasing trend,and the community diversity showed an overall increasing trend,but the community richness showed an increasing trend and then a slow decreasing trend.Alphaproteobacteria and Gammaproteobacteria were significantly positively correlated with cellulose and lignin,but negatively correlated with mass loss(P <0.05).The results of RDA analysis showed that cellulose and available phosphorus were the main driving factors that significantly affected soil bacterial dominant community,while available phosphorus and organic carbon were the main environmental factors that significantly affected soil bacterial diversity.(4)The gene sequences of soil microorganisms have been annotated into six major functions,mainly microbial metabolic functions.Metabolism-related enzymes accounted for about 67% of the total enzymes in each group,and metabolism-related KO accounted for about 32%-34% of the total KO in each group.Among all the metabolic functions that differed significantly between the groups,the biosynthesis of secondary metabolites dominated.The ecological functions of soil fungi are mainly saprophytic and trophic,containing 14 single ecological functional groups and 43 mixed ecological functional groups.Wood saprophyte increased first and then decreased with the increase of time,and reached the maximum value in 7 years,which was 7.41 times of that in 1 year.In the soil bacterial functions of sand barrier decay process,chemoheterotrophy and aerobic chemoheterotrophy were the main functions,while ureolysis,cellulolysis,nitrogen fixation and ligninolysis were auxiliary functions.With increasing decay,both soil cellulolysis and ureolysis showed a decreasing trend,and the total abundance of cellulolysis was greater than that of ligninolysis.