Impact Of Soil Microbial Community Structure On Rotation Cropping And Continuous Cropping Systems Of Typical Crops In Black Soil

Soil microorganism is an important part of soil ecosystem and plays an engine role in the process of decomposition of soil organic matter,nutrient cycling and soil-borne diseases.Soil microbial community structure is primarily influenced by agricultural management practices in agroecosystems.Continuous cropping and crop rotation are the most important primary agricultural practices.Under the conditions of continuous cropping and crop rotation,the soil ecological environment changes due to the combination of single crops and multiple crops,which leads to corresponding changes in the soil microbial community structure and then affects the soil ecological function.At present,systematic studies on the effects of long-term continuous cropping on soil microbial community structure and related functional microbial community structure are rarely reported.Soybean,maize and wheat are the main dryland crops planted in the black soil region of the Northeast,therefore,a systematic study on the effects of continuous cropping and rotation on soil microbes in three typical dryland crops in the black soil region was carried out based on a 27-year field experiment.Biolog,qPCR and Illumina Miseq were used to systematically study the carbon source metabolism characteristics of soil microorganism,the community structure of the soil bacteria,fungi,nitrogen-fixing bacteria and alkaline phosphatase gene,and responsive changes in potentially functional bacteria and functional fungi under long-term continuous cropping and rotation of soybean,maize and wheat in the black soil region of Northeast China.The main conclusions were as follows:(1)There were significant differences in soil microbial metabolic function between long-term continuous cropping and rotation of soybean,maize and wheat.The soil microbial metabolic activity was significantly decreased after long-term continuous cropping in three typical dryland crops.The utilization rate of sugar substances by soil microorganisms was significantly lower in long-term continuous soybean and wheat cropping than that in soybean and wheat rotation,the utilizationrate of polymer and amine substances by soil microorganisms was significantly lower in long-term continuous maize cropping than that in maize rotation.Soil microbial communities had significant differences in carbon utilization among the three crops.(2)Long-term continuous cropping of soybean,maize and wheat had significant effects on soil bacterial community structure.Long-term continuous cropping significantly decreased the relative abundance of C and N-related dominant functional genera(Nocardioides,Pseudonocardia,Pseudolabrys,Nitrospira and Rhizobium,etc.).The bacterial diversity was significantly decreased in long-term continuous cropping of three crops compared with crop rotation systems.There was significant difference in bacterial community structure between long-term continuous cropping and crop rotation,and the variation in the bacterial community structure among the three crops was greater than that between long-term continuous cropping and crop rotation.Soil pH was the soil factor affecting the soil bacterial abundance,diversity and community structure.(3)Long-term continuous cropping of soybean,maize and wheat had different effects on soil fungal community structure.Long-term continuous soybean cropping increased the soil fungal abundance compared with soybean rotation,and the fungal abundance was decreased in long-term continuous maize cropping compared with maize rotation,while there was no difference in fungal abundance between long-term continuous wheat cropping and wheat rotation.The fungal community diversity were significantly higher in long-term continuous soybean cropping than that in soybean rotation.There was significant difference in fungal community structure between long-term continuous cropping and crop rotation.The difference in fungal community structure among the three crops was greater than the difference between long-term continuous cropping and crop rotation.Long-term continuous cropping caused changes in the relative abundance at the genus level.The relative abundance of potential pathogens(Fusarium,Cylindrocarpon,Gibberella,etc.)was significantly higher in long-term continuous cropping of three crops than that in rotation systems.The relative abundance of potential beneficial fungi(Mortierella,Purpureocillium and Accremonium,etc.)was significantly higher in long-term continuous soybean cropping than that in soybean rotation,while that in long-term continuous maize and wheat cropping(Pureocillium,Metadycorps and Metarhizium,etc.)was significantly lower than that in maize and wheat rotation.Soil pH was a significant factor affecting the soil fungal community structure.(4)Long-term continuous cropping of soybean,maize and wheat changed the soil diazotrophic community structure.The diazotrophic abundance was significantly higher in long-term continuous soybean cropping than that in soybean rotation,while the diazotrophic abundance was significantly lower in long-term continuous maize and wheat cropping than that in maize and wheat rotation.Proteobacteria and Bradyrhizobium was the dominant phylum and genus with the highest relative abundance among the three crops.Long-term continuous cropping of maize and wheat significantly decreased the relative abundance of Bradyrhizobium.Soil pH was the most important soil factor affecting the diazotrophic community structure.(5)Long-term continuous cropping of soybean,maize and wheat changed the community composition of alkaline phosphatase gene at genus level.Long-term continuous soybean cropping decreased the relative abundance of Afipia,long-term continuous maize cropping decreased the relative abundance of Amycolatopsis and Acidovorax,and long-term continuous wheat cropping decreased the relative abundance of Pseudomonas and Stenotrophomonas.The alkaline phosphatase gene community structure of wheat had significant difference between long-term continuous cropping and crop rotation.The alkaline phosphatase gene community structure was significantly different among long-term continuous cropping of the three crops.