| Fire is a common environmental perturbation in forest environment.Heat from fire has strong direct or indirect effects on vegetation,animals,soil,regional climate and the water cycle.As an important part of the forest ecosystem,soil microorganisms play a crucial and unique role in energy flow,circulation of material,and maintenance of the balance of the ecosystem.In the burned area of Pinus tabulaeformis forest in Pingquan,Hebei Province,the diversity,community characteristics and influencing factors of soil microbe after different severity burning(in three years)were analyzed.The purpose of our research is to provide theoretical basic for the restoration and reconstruction of forest ecosystem after burning.The study area was classified into different severity levels according to the smoked height and tree mortality;high-severity sites(H),middle-severity sites(M),low-severity sites(L)and nearby unaffected sites(contrast,C).Three 20m×20m sample plots were established under different fire severities.The vegetation composition was investigated and soil samples were collected from September to October in 2015-2017.We utilized Illumina MiSeq sequencing(bacteria:16S;fungi:ITS)to illustrate the changing patterns of the soil microbe after the fire.At the same time,some related software or programs were used to make a prediction of the soil microbial functional composition.Molecular ecological network analysis was also applied to analyze the network structure of soil bacteria and fungi after the burning.The main conclusions are as follow:(1)Fire caused significant changes in aboveground structure with the decrease of canopy density and variation of understory vegetation.The species and diversity of vegetation increased in the high-severity wildfire areas.However,the evenness index showed a decline.Fire has a significant effect on soil physical and chemical properties.We observed a decrease of soil fertility but an increase of soil moisture and pH in the early period after the fire.But,with the revegetation of plant,the content of soil organic matter increased,while the nitrogen was still at a low level(2)Acidobacteria,Proteobacteria,Actinobacteria were the dominant phyla among all samples,which accounted for 70.16%,70.93%and 71.36%of the total bacterial abundance in 2015,2016 and 2017,respectively.The dominant phyla of soil fungi in research areas were Ascomycota,Basidiomycota and Zygomycota,which accounted for 96.94%?95.45%of the total fungal abundance in 2016 and 2017,respectively.More significant differences of bacterial abundance were found between the topsoil and subsoil in the high-severity wildfire areas.However,these differences gradually decrease with time passes.On the other hand,little differences of fungal relative abundance were observed between the different soil layers(3)The effects of fire on the alpha diversity of soil bacteria and fungi were not universal.The changes of soil bacterial or fungal diversity were usually observed in the topsoil where were burned with a high-severity wildfire.The results of NMDS showed that there were significant differences in bacterial community structure between topsoil and subsoil at the early stage after a fire.PCA analysis showed that there was little difference in fungal community structure between two soil layers,but great differences among different fire severity areas were found in separate soil layers.RDA and VPA results indicated that soil physical and chemical properties were the main factors driving the changes of soil microbial community structure in the study area(4)PICRUSt function prediction showed that the main functional types of soil bacteria in the study area were membrane transport,amino acid metabolism and carbohydrate metabolism.FAPROTAX function prediction indicated that the most functional types of bacteria were chemoheterotrophy,nitrogen decomposition and synthesis(nitrification,denitrification,nitrogen respiration,nitrite respiration,etc.)and phototrophy.FUNGuild function prediction showed that the fungi after fire were mainly undefined saprotroph fungi,ectomycorrhizal and endophyte fungi Difference analysis showed that the difference of soil bacterial and fungal functional types between two soil layers will gradually decrease over time(5)Molecular ecological network model shows that the structure of soil bacterial molecular ecological network varies among different years after burning.However,with the increase of time,the model structure tends to be complex and stable.In the early stage after burning,the OTUs of bacteria were mostly positively correlated(synergistic and cooperative),and then negatively correlated(competitive and antagonistic)accounted for more and more.There are dynamic changes in the relationship among bacterial OTUs.Soil physical and chemical properties are the main factors affecting the structure of bacterial molecular ecological network in the study area,and the relationship between bacterial OTU and environmental factors(positive and negative ratio)is different between different years. |
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