Monoculture And Organic Amendment Change Soil Properties And Rhizosphere Microflora In Cucumber And Tomato Greenhouses

Monoculture is common in China for vegetable production under protected cultivation system..Rhizosphere bacterial and fungal communities are considered critically important for plant health.They are affected by environment factors in soil.The environment of greenhouse is different from that in open fields.Usually excessive fertilizers were used to get high yield,leading to the change of soil properties.Cucumber and tomato are important vegetables in China,which are suffering the severe replanting problems.Previous studies focused on how microflora changed as crops monoculture,or how microflora changed with different soil properties.However,few studies combined these two factors together.To explain the change of microbial communities in response to long-term monoculture under soil properties dramatic change,soil samples were collected from greenhouses with different years of cucumber and tomato monoculture.Soil fungal and bacterial community composition and diversity were analyzed using a bar-coded pyrosequencing technique for ITS and 16S rDNA sequences combined with quantitative PCR.In experimental condition,organic fertilizer was applied to treat the monoculture cucumber to demonstrate its effect on successive obstacle and microflora.Results show:(1)Soil properties including soil organic matter(SOC),total nitrogen(TN),total phosphorus(TP),available nitrogen(AN),increased significantly with monoculture years in cucumber greenhouses.SOC ranged from 7.84 to 67.17 g/kg.Soil TN and AN ranged from 1.35 to 8.54 g/kg and from 187.21 to1295.26 mg/kg,respectively.TP content ranged from 0.014 to 0.243%.Soil EC increased(42.5~1632?s/cm)indicating soil salinized gradually.pH(4.28~6.45)firstly decreased and then increased as cropping years increase.The contents of organic matter and nitrogen in monoculture tomato soil first accumulated with the cropping years,and then decreased in longer monoculture soil.The content of phosphorus and potassium was higher than that of cucumber soil.Most soil samples have EC values less than 800?s/cm.(2)In cucumber soil,bacterial abundance ranged from 2.13×10~8 to 5.11×10~9 copies/(g dry soil)and the fungal abundance ranged from 6.70×10~5 to 2.88×10~8/(g dry soil).While,in tomato soil,bacterial abundance ranged from 1.61×10~9 to 10.90×10~9 copies/(g·dry soil),and fungal abundance ranged from1.84×10~7 to 10.50×10~7 copies/(g·dry soil)They both had increasing trend as continuous years due to the accumulation of nutrients.(3)Cucumber rhizosphere microbial diversity decreased with the cropping years.EC was the main factor here to reduce the diversity of both fungal and bacterial diversity.Soil acidification decreased soil bacterial diversity but had no effect on fungal diversity.Cucumber rhizosphere bacterial diversity increased as pH increasing.(4)Monoculture longer than 20 years did not accumulate high level of pathogen Fusarium.The OTUs related to Fusarium in 25 years cropping group declined to amount lower than 3 cropping years group.This was associated with high abundance of antifugal bacterial OTUs related to Bacillus,Pseudomonas and Streptomyces,pH increasing,and organic matter accumulation.(5)The greenhouse experiment showed that applying organic fertilizer to the soil could alleviate the cucumber successive cropping obstacle and reduce the relative abundance of Fusarium.The application of organic fertilizer changed the community of fungi and bacteria in rhizosphere of monoculture cucumber and had a greater effect on the fungi in short term application.This study provided us more clues and basis to amend the soil and improve microbial community to alleviate monoculture obstacle.