Mechanism Of Improvements Of Soil Quality And Tomato Fruit Quality By Vermicompost In Greenhouse

Tomato?Lycopersicon esculentum Mill.?is a main vegetable planted in greenhouse in north China.The most serious problem in the cultivation of tomato is continuous cropping obstacle.Under the scenario of continuous cropping obstacle,the quantity and quality of tomato fruit deceased,soil microenviroment was not suitable for microbe growth.Thus,how to improve soil health,especially soil microbial diversity,is of high importance.Vermicompost,which is an natural and ecological manure,is superior than conventional organic fertilizers in improvement of soil quality.Most of the previous studies suggested that those positive effects of vermicompost result from the improving of soil properties,the input of plant growth promoting materials and the increased defense capacity of plant.However,few studies focus on the impact of vermicompost on soil microbial community structure.In this study,we selected three soils with different tomato continuous cropping durations,0 year,5 years and 20 years,to study the effects of different fertilizer practices on tomato growth,yield,soil physicochemical properties,soil enzymes and soil microbial community.Four treatments were included:chemical fertilizer?CF?,rice straw?FS?,chicken manure?CM?and vermicompost?VM?.These results showed that:1.Soil pH?decreased by 1.23 unit from 0-year soil to 20-year soil?and C/N?decreased by 6.46%and 8.33%in 5-year and 20 year-soil compared with 0-year soil,respectively?decreased,but electrical conductivity?EC?increased under long-term tomato cultivation?increased by 26.75%from 0-year soil to 20-year soil?.The activities of soil catalase and polyphenol oxidase?PPO?decreased,while the activites of urease and acid phosphatase?AcP?increased with the increase of tomato continuous cropping duration.Planting of tomato significantly decreased the numbers of bacteria and actinomycetes as well as the ratios of bacteria to fungi and actinomycetes to fungi and soil microbial diversity,while significantly increased the number of fungi?increased by 49.6%and 59.22%in 5-year and 20-year soilscompared with 0-year soil?and Fusarium oxysporum f.sp.Lycopersici?Fol??increased by 820%and 2804%in 5-year and 20-year soilscompared with 0-year soil?.Tomato fruit yield,organic acid content,soluble sugar content,Vc content and the ratio of sugar to acid significantly increased;however,the content of nitrate significantly increased concurrently.2.Fertilization treatments significantly decreased soil pH and increased soil EC value,irrespective of tomato continuous cropping histories.During the whole growth period of tomato in all the three soils,the soil pH treated with vermicompost was higher than that of CM,FS and CF treatments.All the nutrients and microbial biomass C and N were enhanced under the four treatments.However,the ratio of C/N significantly decreased in all treatments compared with CK,and it decreased less in VM treatment than other treatments.The highest activities of PPO,catalase and AcP were observed under VM treatment,and PPO was significantly lower under CF treatment than CK,regardless of tomato cropping duration.No significant difference of urease avtivity was found between the four treatments in the 0-year and 20-year soils.The highest activity of urease was found under CM treatment which significantly higher than other treatments in 5-year soil.3.The number of bacteria was higher under VM treatment than other treatments,while relative higher fungi number was found under CF and FS treatments.The bacterial?-diversity decreased with the increase of tomato continuous cropping duration.VM treatments hold the highest?-diversity irrespective of continuous cropping duration.The dominant bacteria was significantly different between all the three soils and four treatments.Compared with CF treatment,VM and CM treatments significantly improved soil microbial community structure.Correlation analysis revealed that soil pH and soil organic matter?OM?were the strongest drivers of soil bacterial community structure.The Chao1 index of fungi decreased,while the Shannon and Simpson indexes firstly decreased and than increased with the increase of continuous cropping duration.The relative lower fungal diversity was found under CM treatment,while the relative higher fungal diversity was found under VM treatment in all the three soils.Similar with bacteria,soil pH and OM play the important roles in the shaping of fungal community structure.4.Vermicompost was the most effective organic fertilizer to suppress Fol in long-term continuous tomato cropping soil?the inhibition efficiency was 44.42%?.Structural equation modeling?SEM?revealed strong relationship between the relative abundance of family Acidimicrobiaceae and genus Ilumatobacter with Fol inhibition.Soil pH and NH₄⁺-N positively promoted the development of family Acidimicrobiaceae and genus Ilumatobacter.Vermicompost addition increased pH and NH₄⁺-N concentration in soil with longest continuous cropping duration.Most important,family Acidimicrobiaceae and genus Ilumatobacter enriched in vermicompost,which may contribute to the propagation of these bacteria in soil.5.VM and CM treatments both promoted tomato plant growth which including plant height,stem diameter,root activity,root dry weight and shoot dry weight.Compared with CK,the best fruit quality was found under VM treatment in all the three soils.The positive effects of VM on fruit yield and quality were more obvious in soil with short continuous cropping duration than with long continuous cropping duration.Compared with CK,fruit yield,Vc content,soluble sugar,the ratio of sugar to acid and nitrate increased by 74%,47%,71%,210%and 31%under VM treatment,respectively.In conclusion,vermicompost was the most effective organic fertilizer in the improving of soil fertility and structure.Furthermore,vermicompost could be used to control soil pathogen by the inducing of beneficial microorganisms,especially in soil with long-term continuous cropping duration.This study provided a mechanistic framework that permitted to explore specific function at lower taxonomic levels which harbor novel potential for the management of crop pathogen by means of promoting beneficial organisms.