Effects Of Different Land Use Patterns On Soil Bacterial Community Structure In The Mollisol Region Of Northeast China

The Mollisol region of Northeast China plays an important role in ensuring national grain security.In recent years,the fertility of black soil has been severely overdrawn due to high-intensity human utilization.And unreasonable land use is the key factor that aggravates environmental risks of black soil ecosystem and accelerates the decline of soil quality.Soil microorganisms are important indicators of soil quality and play a key role in soil nutrient cycling,pollutant degradation,and disease inhibition.Based on the long-term positioning experiment of the Hailun Monitoring and Research Station of Soil and Water Conservation of Chinese Academy of Sciences,five land use patterns were selected:conventional tillage,no-tillage with straw mulching,grassland,forest and bare land.The spatial distribution characteristics of soil bacterial community composition and diversity under different land use patterns were compared and analyzed using Illumina high throughput sequencing technology,and the dominant factors affecting the soil bacterial community structure in the Mollisol region of Northeast China were revealed.This study provides data support for formulating reasonable and effective strategies and measures of the black soil conservation and utilization.（1）The soil p H value was between 5.93-6.86,which increased with depth in conventional tillage,bare land and forest.The soil moisture content（SWC）in no-tillage with straw mulching and grassland was significantly higher than other land use patterns at 0-5 cm（P<0.05）.The soil bulk density（SBD）of bare land increased with depth,which was significantly higher in forest than bare land at 0-5 cm,5-10cm and 10-20 cm（P<0.05）.The contents of total organic carbon（TOC）and total nitrogen（TN）decreased with depth in conventional tillage,bare land,no-tillage with straw mulching and grassland,which were significantly lower than other land use patterns in bare land at 5-10 cm and 10-20 cm（P<0.05）.The content of ammonium nitrogen（NH₄⁺-N）was significantly higher in conventional tillage and no-tillage with straw mulching than bare land（P<0.05）,while the content of soil nitrate nitrogen（NO₃^--N）was significantly higher in forest than conventional tillage at 5-10cm,10-20 cm,and 20-30 cm（P<0.05）.The total phosphorus（TP）content was significantly higher in bare land than no-tillage with straw mulching（P<0.05）.（2）The ACE,Chao1 and Shannon indices of soil bacterial communities in no-tillage with straw mulching were significantly higher than forest at 0-5 cm（P<0.05）,while the Shannon index in no-tillage with straw mulching was significantly higher than bare land at 5-10 cm and 10-20 cm（P<0.05）.The results of PCo A showed that the soil bacterial community structure was similar between forest and grassland,which was similar in conventional tillage,bare land and no-tillage with straw mulching.The dominant phylum included Actinomycetota,Proteobacteria,Acidobacteriota,and Chloroflexota.The relative abundance of Actinomycetota in bare land was significantly higher than no-tillage with straw mulching,grassland and conventional tillage at 0-5 cm and 5-10 cm（P<0.05）.The relative abundance of Proteobacteria in no-tillage with straw mulching was significantly higher than that in bare land（P<0.05）,which decreased with soil depth.The results of functional prediction analysis showed that there were eighteen secondary functional metabolic pathways of soil bacteria with relative abundance greater than 1%under five land use patterns,among which carbohydrate metabolism and amino acid metabolism differed significantly between different land use patterns（P<0.05）.（3）The results of Pearson analysis showed that the ACE,Chao1 and Shannon indices were significantly positively correlated with TOC,TN and NH₄⁺-N,while the Simpson index was significantly negatively correlated with TOC,TN and NH₄⁺-N（P<0.05）.The RDA results showed that eight environmental factors explained71.79%of the variation of dominant bacterial community structure at the phylum level.Proteobacteria and Bacteroidota were significantly positively correlated with TOC,TN,SWC and NO₃^--N.Actinomycetota has significant correlations with TOC,TN,SWC,p H,NH₄⁺-N and TP.Firmicutes was significantly positively correlated with NH₄⁺-N.