| Torreya grandis cv.Merrillii is a unique rare nut tree species in Zhejiang Province of China,which has high nutritional value and high price.With the continuous expansion of planting scale,the unscientific management modes induced microecological imbalance,and root rot soil borne disease is increasingly prominent,which caused huge losses to forestry production and economy in Zhejiang Province.Revealing the soil microecological mechanism of occurrence of Torreya grandis cv.Merrillii root rot has important theoretical and practical significance for improving soil quality of Torreya grandis cv.Merrillii plantation and promoting sustainable development of Torreya grandis cv.Merrillii industry.In this study,Torreya grandis cv.Merrillii plantation with high incidence of root rot in Lin'an District,Hangzhou City,Zhejiang Province was taken as the research object.From the perspective of soil microecology,high throughput sequencing technology was used to compare and analyze the root zone soil bacteria and fungi composition of healthy and root rot plants,combined with related plant biomass,physiology and soil physical and chemical characteristics indicators,identified key driving factors affecting soil microbial community composition and activity.By analyzing soil enzyme activities related to carbon,nitrogen,phosphorus and other nutrient cycle and carbon source utilization rate,the soil microbial functional metabolism characteristics were characterized.The interaction mechanism of soil,plant and microorganism during the occurrence of root rot was discussed,which provided scientific basis for revealing the occurrence mechanism and disease control of root rot of Torreya grandis cv.Merrillii.The main findings are as follows:(1)By comparing plant growth physiological indexes of healthy and diseased Torreya grandis cv.Merrillii,it was found that tree height,shoot biomass and root biomass,leaf moisture content,chlorophyll and nitrogen content decreased significantly.However,the activity of peroxidase(POD)increased significantly.Comparing the root zone soil physical and chemical properties of healthy and diseased plants,it was found that the organic carbon(SOC)content in the diseased plant soil decreased significantly,while pH,moisture content and available nitrogen content increased significantly in the diseased plant soil.(2)The root zone soil microbial community characteristics of healthy and diseased Torreya grandis cv.Merrillii plants were compared and studied.The results showed that bacteria and fungi abundance in the diseased plant soil was 52.10% and 70.08% lower than healthy plant soil,and the diversity indices were not significantly difference.There were significant changes in fungal community composition and no significant changes in bacterial community.Proteobacteria,Acidobacteria,Actinobacteria were the main bacteria phylum,and the relative abundance of Proteobacteria was significantly decreased by 19% in the diseased plant soil.Ascomycota and Basidiomycota were the main fungi phylum.The relative abundance of Zygomycota in diseased plant soil was significantly increased by 135% than healthy plant soil.The relative abundance of Gibberella,Cryptococcus,Didymella,Mortierella and Agaricales_unclassified in the diseased plant soil was 90.2%,124.3%,34.7%,114.6% and 824.0% higher than healthy plant soil,respectively.They were believed to be the key genus which cause the change of fungal community composition and were considered to be related probably to the occurrence of root rot.(3)The root zone soil enzyme activity and microbial metabolism function of healthy and diseased Torreya grandis cv.Merrillii plants were compared and studied.The results showed that metabolic activity of microorganism has changed and utilization rate of microbe to carbohydrate was improved significantly in diseased plant soil.The metabolic function diversity indices(Shannon index and Simpson index)in the diseased plant soil were significantly higher than healthy plant.The activities of peroxidase,?-D-cellulosidase,?-glucosidase and arylsulfatase in the diseased plant soil were significantly higher than healthy plant,while the activity of phosphatase was significantly lower than healthy plant.(4)Further analysis on the relationship between plant growth,root zone soil properties and soil microbial community of Torreya grandis cv.Merrillii showed that shoot biomass,tree height,root biomass,leaf water content and nitrogen content were negatively correlated with soil moisture content,and positively correlated with soil organic carbon content.The change of bacterial community was significantly correlated with soil available nitrogen content,organic carbon content and root biomass,and fungal community only changed significantly with soil moisture,which were considered to be important abiotic factors that change microbial communities.Root rot,root biomass and soil properties explained 42.3% and 35.2% of the variation of bacterial and fungal communities,respectively,while soil properties explained the maximum variation of bacterial and fungal communities.The enzyme activity in the diseased plant soil was significantly correlated with soil fungi community composition,soil water content and microbial carbon source utilization rate,while the enzyme activity in healthy plant soil was significantly correlated with root biomass and fungal abundance.Soil moisture content and microbial carbon utilization rate were positively correlated with ?-D-glucosidase and ?-glucosidase activities,which explained 14% and 13% of the variation,respectively.In conclusion,prolonged root-rot infestation decreased tree vitality and soil microbial biomass,changed fungal community composition and soil functioning towards a faster organic C decomposition,which potentially may increase soil organic matter turnover.In the later prevention and control work of Torreya grandis cv.Merrillii root rot,we should pay close attention to the change of soil environment and improve soil quality to improve plant disease resistance. |
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