| Soil physicochemical properties and microbial community structure are extremely sensitive to tillage process.Long-term frequent tillage can lead to black soil degradation,soil and water loss and biological characteristics change.However,there is no unified conclusion on the physicochemical properties,enzyme activities,microbial diversity and community structure under long-term tillage in black soil during different seasons,and the coupling relationship among them.In this study,soil samples of uncultivated(unreclaimed)and long-term cultivated(continuous cultivated for 60 years)soils were collected in spring(May),summer(July)and autumn(October)of 2017,respectively.We used conventional soil analysis method to determine the physicochemical properties and enzyme activity and employed Illumina Mi Seq high-throughput sequencing technology to study the diversity,taxonomic composition,and co-occurrence network properties of microbial community,comparing outcomes between uncultivated soil and long-term cultivated soil.Pearson correlation analysis and redundancy analysis were used to study the effects of soil physicochemical properties on microbial diversity and community structure between long-term cultivated soil and uncultivated soil.The purpose of this study is to investigate the response rules of soil microbial diversity and community structure to long-term tillage,and to provide a scientific basis for preventing soil erosion,the protection and restoration of black soil ecosystem by understanding the response mechanism of microorganisms of black soil to long-term tillage.The main research results are as follows:1.The p H,organic matter,total nitrogen contents and the activities of sucrase and acid phosphatase of long-term cultivated soil were lower than those of uncultivated soil,with the decreasing ranges of 6.05%-11.03%,14.16%-16.67%,11.37%-29.84%,33.66%-36.38% and12.14%-21.53%,respectively.The contents of nitrate nitrogen,total potassium,available phosphorus,and available potassium and the activity of catalase in long-term cultivated soil were higher than those in uncultivated soil,with the increase ranges of 67.19%-489.20%,2.00%-7.56%,379.56%-422.60%,43.69%-57.33% and 121.88%-439.62%,respectively.However,there was no significant difference in urease activity in black soil.2.The relative content of water-stable aggregates with large particle size(>1 mm)in long-term cultivated soil decreased by 34.17%-51.37%,and the relative content of >0.25 mm water-stable aggregates,mean weight diameter and geometric mean diameter reduced,while the fractal dimension D and soil erodibility K were significantly increased.3.The alpha-diversity of bacterial community were different in each season.Compared with uncultivated soil,the alpha-diversity index of bacterial community in long-term cultivated soil increased significantly in spring;in summer,there was no significant difference in other indexes except Simpson index;in autumn,the richness of bacterial community decreased significantly while the diversity increased.The richness of fungal and archaeal communities and the diversity of fungal community in long-term cultivated soil were lower than those in uncultivated soil in each season,while the diversity of archaeal community was higher than that of uncultivated soil.Microbial community beta-diversity analysis and co-occurrence network analysis showed that soil fungal community was more unstable than bacterial and archaeal community,which was easily affected by long-term tillage and season.4.The relative abundance of Actinobacteria in long-term cultivated soil decreased markedly,while the relative abundance of Proteobacteria and Gemmatimonadetes increased significantly;the relative abundance of Ascomycetes increased obviously in summer and autumn;the relative abundance of Thaumarchaeota increased,while the relative abundance of Bathyarchaeota was low and only found in uncultivated soils.Pearson correlation analysis showed that Actinobacteria may exist in large particle size water-stable aggregates or promote the formation of large particle size water-stable aggregates,while Proteobacteria and Gemmatimonadetes may exist in small particle size water-stable aggregates or promote the formation of small particle size water-stable aggregates.5.At the genus level,the community structure of bacteria,fungi and archaea in long-term cultivated and uncultivated soils changed noticeably.The relative abundance of Rubrobacter,Bradyrhizobium,Acidothermus,Nitrobacter,Savoryella,Methanosaeta and Methanocella were significantly decreased,which had a certain influence on cellulose degradation,nitrification,nitrogen fixation and methane production in black soil.However,the relative abundance of Pseudomonas,Monographella,Fusarium,Penicillium and Neurospora all increased significantly.Some of these bacteria and fungi are plant pathogens,which have adverse effects on crop growth.At the same time,the relative abundance of Sphingomonas,Blastococcus,Acremonium and Humicola increased,which could promote the degradation of aromatic compounds and improve the ability of plant resistance to pests and diseases.Long-term tillage destroyed the structure of soil water-stable aggregates,promoted the depolymerization of water-stable aggregates with large particle size into water-stable aggregates with small particle size,thus reducing the soil water stability and erosion resistance.Long-term tillage accelerated the mineralization of organic carbon and nitrogen in water-stable aggregates and reduced the contents of organic carbon and nitrogen in the black soil.Moreover,the p H of black soil decreased,which changed the diversity and community structure of microorganisms in the black soil,as well as the relationship among microorganisms,and affected the ecological function of soil microorganisms,thus affecting the nutrient circulation in the black soil.Soil p H was the main driving factors affecting the bacterial diversity and community structure;soil available phosphorus and p H were the main driving factors affecting fungal and archaeal community diversity and community structure. |
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