| The slash-burning woodland renewal management model of single tree species and multi-generation continuous planting of eucalyptus plantation has caused severe disturbance to the soil quality and ecological environment,which has aroused widespread concern in the society,and the adoption of the model of non-refining mountain afforestation is one of the important measures to solve the above problems.However,under the non-Lianshan afforestation model,how does the soil microbial community,as an important part of the soil ecological environment,respond,and what kind of dynamic changes will occur in four different years after woodland regeneration?We still know very little.In order to avoid the new afforestation model of slash-burning woodland renewal as the research object,this paper analyzed the dynamic changes of bacterial community structure and function in eucalyptus plantation soil under different cutting residue treatment methods in different years after forest land regeneration.The subjects were randomized block trials of four different treatment methods of cutting residues:slash-burning woodland renewal,removal of cutting residues,flat cutting residues and banded stacking of cutting residues,and compared with the third generation eucalyptus plantation before cutting and the coniferous and broad-leaved mixed secondary forest near the sample plot,the soil physical,chemical and biological properties were studied based on the results of 16srna sequencing.The dynamic changes of soil bacterial community structure and diversity were analyzed,and the gene function of soil bacteria was predicted.The main conclusions are as follows:(1)Using high-throughput sequencing technology,7358 OTU were identified.Through the index difference test of analysis of variance,the a diversity index and richness index of bacterial community(Shannon diversity,Simpsion evenness,Ace richness,Chao richness)between different cutting residues treatment and sampling time were revealed.In this study,it was found that the biggest difference among different cutting residue management methods in a diversity index was that the extreme values of Shannon diversity and Simpsion evenness index appeared in the index values of pre-cutting and secondary forest respectively,and mountain refining and removal treatments caused relatively greater disturbance to soil bacterial community in the early stage of woodland regeneration.Because in the first year after forest land regeneration,the shannon index values of mountain refining and removal treatments were both lower than those of pre-cutting and secondary forests,while the values of Simpsion evenness index of refining and removal treatments were higher than those of pre-cutting and secondary forests,and in the Chao richness index,the values of refining and removal indexes of the first year were lower than those of paving,refining,pre-cutting and secondary forests.In addition,according to the comparison of different planting years index values after woodland regeneration,it was found that there were the most significant differences in index values between the first year and other years.Through ?-diversity analysis and PERMANOVA analysis,we found that different cutting residue management methods had limited effect on the change of soil bacterial community(p<0.05).(2)Through the analysis of the venn map of soil bacterial community,we further found that woodland regeneration will cause great disturbance to soil ecological environment,and in different cutting residue management methods,removal treatment may have the greatest disturbance to soil bacterial community,so there are the most unique OTU in removal treatment.In the VENN map of soil bacterial community in different years after woodland regeneration,we found that the soil bacterial community could not return to a relatively stable state in the first year of disturbance.(3)The relative abundance of bacterial community in soil showed dynamic changes in different cutting residue treatment methods and different years.Proteobacteria(relative abundance 28.7%?40.5%),Acidobacteria(20.9%?38%)and Actinobacteria(6.8%?16.9%)could become the dominant flora with relative abundance more than 5%in different cutting residue management methods and different years.However,Chlorooflexi(4?20.5%)and Firmicutes(1.5%?6.2%)could not be the dominant flora in some cases.(4)In the soil properties,the physical and chemical properties fluctuated within two years after woodland regeneration and tended to be stable.in the fourth year,there was no significant difference in the physical and chemical properties among the four cutting residue treatments,but in the biochemical properties,the high value of sucrase appeared in the tiling treatment,the lowest tended to appear in slash-burning woodland renewal and removal treatment,and the high value of urease tended to appear in slash-burning woodland renewal treatment.(5)The results of Heatmap analysis showed that soil chemical properties affected bacterial communities with an average relative community ratio of more than 2%.It was found that there was a significant correlation between environmental factors such as organic matter,total potassium,total phosphorus,calcium,magnesium and urease activity and soil bacterial communities,suggesting that these soil environmental factors may be the key limiting factors for the change of soil bacterial community structure.(6)The functional prediction of bacterial community found that the differences among different treatment methods of cutting residues mainly existed between pre-cutting and secondary forests.Among them,the pathways with low expression in pre-cutting treatment are functional genes that become important only when the soil environment is unstable.Among the different years after woodland regeneration,the pathways with high expression are related to the rapid development and expansion of bacterial communities,and even the possible succession of some bacterial communities is also related to the large expression of these functional genes. |
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