Effects Of Different Human Disturbance Intensity On Bacterial Community In Karst Area In Southwest China

Soil microorganisms play a key role in maintaining ecosystem functions and stability,and are highly sensitive to environmental changes.Bacteria are the most abundant group of microorganisms.In this study,high-throughput sequencing was used to study the effects of different disturbance intensity on bacterial communities and interactions in bulk and rock-soil interface soil in karst areas.In this study,four land use types,including primary forest,secondary forest,abandoned land and cultivated land,were selected.The results show that:(1)Soil organic carbon(SOC),total nitrogen(TN),magnesium(Mg),aluminate(Al)content and C/N presented a decreasing trend along the increasing of disturbance intensity;the ammoniacal nitrogen(NH4+-N),nitrate nitrogen(NO3--N)and calcium(Ca)content in primary forest was significantly higher than that in other three land use types.The dissolved organic carbon(DOC)content in secondary forest and abandoned land was higher than in primary forest and cultivated land.The content of DOC in the secondary forest and abandoned cultivated land was about 15.4-60.4% higher than that in the original forest and cultivated land.The p H value in secondary forest was the highest.The phosphorus(P)content in secondary forest was significantly lower than the other three land use types.The SOC content of the rock-soil-interface in primary forest and abandoned land was significantly higher than in the bulk soil.The contents of DOC,NH4+-N and Ca in the rock-soil-interface were significantly higher than those in the bulk soil in primary forest,abandoned land and cultivated land.Under the four land use types,the Al contents in the rock-soil interface soil were significantly higher than that in the bulk soil.Under each land use mode,the p H value in the rock-soil interface soil is higher than that in the massive soil of 14.0-20.3%.This study shows that different disturbance intensity affect the physical and chemical properties of soil,and rocks also affect the physical and chemical properties of rock-soil interface(2 cm far away from rock)and bulk.(2)Different disturbance intensity significantly affect the bacterial relative abundance and community structure,and it also have significant effects on the bulk and the rock-soil-interface.The soil bacterial phylotype richness and Shannon index of abandoned land and cultivated land were significantly higher than those of primary forest and secondary forest.In cultivated land,the soil bacterial phylotypes richness and Shannon index in rock-soil-interface were significantly higher than in bulk soil.Phylotype richness and Shannon index were negatively correlated with soil SOC,TN,C/N,Mg and Al contents,and positively correlated with sulphur(S)contents.There was a positive correlation between Shannon index and DOC content.With the increase of disturbance intensity,the relative abundance of Proteobacteria,Actinomycetes and Verrucomicrobi decreased,while the relative abundance of Acidobacteria,Bacteroidetes and Chlorobacteria increased.The difference of relative abundance of major groups between rock-soil-interface and bulk soil is mainly showed in abandoned cultivated land.There were significant differences in soil bacterial community structure between any two land use types except abandoned land and cultivated land.In the highly disturbed land(abandoned land and cultivated land),the bacterial community structure of rock-soil-interface and bulk soil is significantly different.Soil SOC,Mg,Al and S contents and p H values significantly affected the bacterial community structure.(3)With the decrease of disturbance intensity,the network of soil bacterial community tended to be larger and more complex,the average path length and modularity of the network tended to decrease,while the average clustering coefficient tended to increase;under the four land use types,the bacterial groups tended to be co-occurrence.Compared with primary forest and abandoned land,there are fewer key species that connecting different functional groups in secondary forest and cultivated land,The bacterial network of bulk soil is larger than in rock-soil-interface,and the operational taxonomic unit(OTUs)in bulk soil is closer.After disturbed,the information can be transmitted to the whole network more quickly.In the rock-soil interface soil,there are fewer bacterial groups connecting the linksbetween modules than in the bulk soil,and the key species in the bulk soil mostly play the role of connecting modules to form the network.