Dynamics Of Soil Microbial Community During Fire Chronosequences In Pinus Vunnanensis Forest In Central Yunnan

Fire is an important disturbance factor in forest ecosystems.Forest fires not only destroy the forest vegetation,but also affe Pinus yunnanensis ct soil ecological processes.Yunnan Province has widely distributed coniferous forests,which is a hotspot of forest fires in China due to dry climatic profile.However,there are few studies on how fire affects the dynamics of soil microbial community in Pinus yunnanensis forest,and relevant research can provide scientific evidence for the recovery and management of Pinus yunnanensis forests after fire.This thesis took Pinus yunnanensis forest in Yimen County,Yuxi City,Yunnan Province as the research object,and selected six Pinus yunnanensis forest fire sequence plots 0 year(fire in the current year),1 year,3 years,7 years,12 years and 25 years after fire.At the same time,the plots with similar conditions but not burned were selected as control near the burning plot.Soil physical and chemical properties,enzyme activities,fungi and bacteria were measured to analyze the dynamic changes and influencing factors of soil microbial community Pinus yunnanensis forest.The main results are as follows:(1)Soil physicochemical properties and enzyme activity under fire sequenceIn this thesis,12 soil physicochemical properties such as soil organic carbon(SOC),total nitrogen(TN),total phosphorus(TP),microbial biomass carbon(MBC),carbon nitrogen ratio(C/N),pH,nitrogen phosphorus ratio(N/P),available phosphorus(AP),nitrate nitrogen and soil water content(W)were measured.Compared with the control group,AP,TN,C/N increased significantly after fire,while MBC decreased significantly,PH value increased significantly and then decreased significantly and then increased again.The ratio of W and N/P decreased significantly after fire,and TP increased significantly first and then decreased significantly after fire.The sampling site was set as a random factor and the linear mixing model was established.The results showed that the N/P and C/N values decreased significantly due to fire effect.The values of C/N and N/P decreased significantly,while SOC,soluble organic carbon(DOC)and ammonia nitrogen(NH4+-N)increased significantly.In this thesis,seven soil enzymes were measured,including medium manganese peroxidase(MnP),β-D-cellulose diosaccharide hydrolase(CBH)and β-Xyl.The activities of p-xyl and MnP were significantly increased by fire.The sampling site was set as a random factor,and the linear mixing model was established.The results showed that the CBH enzyme activity was significantly decreased by the burning sequence.(2)Changes and influencing factors of soil microorganisms under fire chronosequencesAfter fire,in funthe number of Basidiomycota decreased and then increased significantly.Ascomycota significantly decreased,while Glomeromycota significantly increased.After fire,Acidobacteriota,Chloroflexi and Actinobacteria were significantly increased,Proteobacteria were significantly decreased first and then increased,Verrucomicrobiota was significantly decreased,Myxococcota were significantly decreased first,then increased and then decreased.After fire,the alpha diversity index of microorganisms decreased significantly,and the community structure changed.The sampling sites were set as random factors,and soil microorganisms were used as response variables to build a linear mixture model.The results showed that fire effect reduced the Ascomycota of fungi,significantly increased the Mucormycota,and increased the Gemmatimonadetes and Actinobacteriota of the bacteria.The relative abundances of Verrucomicrobiota,Proteobacteria and Acidobacteria increased with time.The differential microorganisms of fungi after burning were Basidiomycota and Ascomycota,while the differential microorganisms of bacteria were Acidobacteria,Chloroflexbacteria,Firmicutes,Verrucomicrobia and Proteobacteria.Under the fire sequence,DOC,CBH and β-Xyl affect the fungal community,and DOC,NO3--N,SOC,NH4+-N,CBH affect the bacterial community.The factors affecting the bacterial community under the fire effect were DOC,NO3--N,AP,SOC,TP,and TN,Fungi had no significant influence.In this study,the method of space-for-time substitution(fire chronosequences)was used to explore the changes of microorganisms and the relationship between microorganisms and soil enzyme activities and soil physicochemical properties during the recovery process after fire.To reveal the mechanism of soil-microorganism action after fire is helpful for the restoration and reconstruction of Pinus yunnanensis forest ecosystem after fire.