Analysis Of Microbial And Viral Diversity In Paddy Soil And Effects Of Long-term Wheat Fallow On Soil Fungal Diversity And Fungal Diseases

Rice is an important food crop in China,with six major rice cropping regions.Soil microbes play important roles in plant growth,but the differences in community structure and function of soil microbes in major rice cropping regions of China are not clear at present.In addition,winter wheat fallow policy has been implemented in North China Plain which is one of the pilot land fallow policies.However,the long-term effects of winter wheat fallow on soil physical and chemical properties,soil microbial diversity and crop diseases are unclear.The soil microbial and viral community structure and function in the three rice-growing regions with different cropping systems were studied,the three rice-growing regions were rice double cropping region in South China,rice-wheat rotation cropping region in Central China and rice single cropping region in Northeast China.The main results were as follows:(1)There were significant differences in soil microbial community structure among the three cropping systems.21% of the dominant genera(relative abundance > 1%)of soil microbial community and 59.51% of soil virus species had regional specificity;(2)The correlation between the abundance of soil viruses and their host bacteria in the three cropping systems is complicated.Among the dominant phage groups(relative abundance > 1%),eight phage groups showed negative correlation with host bacteria,three showed positive correlation,and eight showed no correlation;(3)The soil microbial functions at the three cropping systems were region-specific.Genes related to carbon metabolism were significantly enriched in northeast region and positively correlated with the high content of soil organic matter.Genes related to xenobiotics biodegradation and metabolism were significantly enriched in the central region,which was positively correlated with the large amount of pesticide application.However,genes related to soil toxicity factors were significantly enriched and genes related to biosynthesis of secondary metabolites were significantly decreased in south region,which were positively correlated with the local high temperature and humidity environment.And it was speculated to be the main factor of the occurrence of rice bacterial diseases in south region;(4)Soil viral auxiliary carbon metabolism genes were detected,which was the highest in northeast region,accounting for 67.43% of the total abundance;(5)Enterobacter phage-NJ was isolated and its functions were verified by greenhouse inoculating experiment and 16 S amplification sequencing.The results showed that it could significantly reduce soil nitrogen fixation capacity and change the soil bacterial community structure and function.On the other hand,we studied the soil microbial and viral community structure and function in southwest rice-growing region under two terrains: plateau and basin,and verified the influence of environmental factors by greenhouse pot experiment.The main results were as follows:(1)The richness and diversity of soil microbes in plateau were significantly higher than those in basin;(2)The soil microbial functions in the two regions were region-specific.Genes related to carbon metabolism,secondary metabolite synthesis,especially antibiotic synthesis,were significantly enriched in plateau area,while genes related to energy metabolism,xenobiotics biodegradation and metabolism were significantly enriched in basin area;(3)Through environmental correlation analysis,we found that soil organic matter,nitrogen and potassium were the main factors affecting soil microbial community structure,while temperature was the main factor affecting soil microbial function;(4)The soil viral community structure was different between the two regions,and temperature was the main influencing factor;(5)Soil viral auxiliary metabolic genes were detected in the two regions.The abundance of carbohydrates-related genes in plateau was about 6 times as high as that in basin.In addition,in order to save water resources,the policy of wheat fallow was implemented in north China Plain.In our study,it was found that continuous wheat fallow significantly reduced soil organic matter,nitrogen,phosphorus contents,and the diversity of soil fungal community.It aggravated the occurrence of single parasitic diseases such as maize southern leaf blight and brown spot disease,and reduced the occurrence of trans-parasitic diseases such as maize stem rot.In conclusion,we studied the soil microbial and viral community structure and function in southern,central,northeastern and southwestern regions of China,and verified the role of viruses in assisting soil nutrient cycling and regulating soil microbial community structure and function.The results will contribute to the effective utilization of local natural resources and the healthy and safe production of rice.In addition,the long-term application of wheat fallow can reduce soil fertility,reduce soil fungal diversity and affect the occurrence of fungal diseases,which can provide a theoretical basis for guiding the implementation of wheat fallow.