| Soil quality is crucial to the productivity of terrestrial ecosystem and environmental sustainability,and is a comprehensive reflection of the level and effect of land use management.Land use change can significantly affect soil quality by affecting vegetation composition,soil properties and soil ecological functions.Soil microorganisms are the key drivers of soil ecological functions,and there is a close interaction relationship with soil quality.Therefore,microbial community traits have great potential for soil quality evaluation.Red soil hilly area with excellent water and heat conditions is an important production base for grain,fishery and animal husbandry in our country,but its special geographical location and climatic conditions make the soil in this area very sensitive to human disturbance such as land use change,which brings great challenges to the maintenance of soil quality.In this study,Taihe County of Jiangxi Province,which is located in a typical red soil distribution area,was selected as the research area.Soil samples were collected under two typical land use types(natural forest land and farmland)widely distributed in Taihe County,and high-throughput sequencing analysis and soil quality index method were used.The change characteristics of soil microbial community and soil quality index under different land use types were studied,and the coupling relationship between soil quality index and microbial community characteristics was analyzed,in order to provide scientific basis for soil quality management and sustainable use of land resources in typical hilly areas of red soil,and to facilitate in-depth exploration of rapid evaluation methods of soil quality based on high-throughput sequencing.The main results are as follows:Soil microbial diversity,community composition and molecular ecological network structure were significantly different under different land use types.Compared with natural forest land,the bacterial richness(Chao1 and Sobs),bacterial uniformity,bacterial Shannon diversity and fungal richness in cultivated soil were significantly decreased.There were significant differences in soil bacterial and fungal community structure(β diversity)under different land use and sampling areas.The microbial molecular ecological network in natural forest land and cultivated land soil was significantly different and changed with different sampling areas.In general,the average connectivity of bacterial network in the three sampling areas was forest land >cultivated land,indicating that the soil bacterial network in forest land was more complex.For fungal networks,the average clustering coefficient,average path distance,and modularity were higher in woodland soil at site 1 and site 3,but the opposite was true at site 2.Correlation analysis and Mantel test analysis revealed that soil p H,cation exchange capacity(CEC),dissolved organic nitrogen(DON),dissolved organic carbon(DOC)and soil texture were significantly correlated with soil bacterial and fungal diversity,community composition and structure under different land uses.Distancebased redundancy analysis(db-RDA)further revealed that p H was the environmental factor with the highest explanatory degree for the variation of soil bacterial and fungal community structure in any sampling area,indicating that soil p H was the key factor driving microbial community variation under different land use types.Based on principal component analysis and correlation coefficient among indexes,p H,soil total nitrogen,soil total phosphorus,soil water content,sand content and nitrogen invertase activity were selected as the minimum data set indexes.A total of 8soil quality indexes(SQIs)were calculated by the combination of different index screening,index scoring function and integrated model,and there was a significant positive correlation between these soil quality indexes.The variation coefficients of SQI-W-MDS-L and SQI-N-MDS-L were higher than those of other soil quality indexes,and the values of these two soil quality indexes in natural forest land(0.353 and 0.230,respectively)were significantly higher than those in cultivated land(0.311 and 0.202,respectively).The results indicated that SQI-W-MDS-L and SQI-N-MDS-L were more suitable for evaluating the effects of land use change on soil quality in the study area.The difference of soil quality index under different land use types was closely related to soil microbial community composition.The values of SQI-W-MDS-L and SQI-N-MDS-L increased significantly with the increase of the relative abundance of Gemmatimonadetes and Rokubacteria,but were negatively correlated with the relative abundance of Actinobacteria.Random forest models reveal that the microbial populations that contributed significantly to predicting the difference of soil quality index under different land use types included NC10(Rokubacteria),Dadabacteriia(Dadabacteriia),Gemmatimonadetes(Chloroflexi),Actinobacteria(Actinobacteria)and Kickxellomycetes(Kickxellomycota),Mortierellomycetes(Mortierellomycota),Rhizophlyctidomycetes(Chytridiomycota),etc.In addition,the relative abundance of some key nodes in microbial molecular ecological network(such as connectors and module hubs)is also an important index to predict the variation of soil quality index under different land use types.The key nodes that contributed significantly to the variation of soil quality index mainly belonged to the dominant bacteria and fungi populations such as Proteobacteria,Chloroflexi and Ascomycota.Future studies need to further explore the influence mechanism of these key predicted populations on soil quality. |
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