A Study On The Influencing Factors And After-effects Of Strongly Reducing Soil Treatment

Reductive soil disinfestation（RSD）is consisted of adding a large amount of degradable organic matter to the soil infected by soil-borne pathogens,irrigating soil to saturation and covering it with plastic film.RSD can form an extremely anaerobic environment in a short time,quickly kill soil borne pathogens,improve soil physical and chemical properties,and achieve the purpose of effective control of soil borne diseases.A large number of studies have shown that RSD treatment has a broad-spectrum sterilization effect on soil borne pathogens,can control plant diseases in a variety of crop planting systems,improve soil microbial community structure,and can also improve soil acidification,hardening,salinization and other problems.However,it is still unclear whether the effect of RSD treatment is different under different types of organic materials,different soil properties and different utilization methods.After RSD treatment,the changes of soil pathogens and soil microbial community structure in the process of crop replanting were also lack of in-depth research.Based on Real-time PCR and Mi Seq amplicon sequencing techniques,this study selected the greenhouses usually planted with leafy and fruit vegetables as research subjects.Field experiments were conducted to evaluate（1）the effects of different soil properties,different soil use patterns and different materials on the remediation of continuous cropping obstacle by RSD,（2）the effects of RSD treatment on crop growth,changes of soil physicochemical and microbial properties during the following two planting seasons after RSD,（3）the effects of RSD and crop planting on the bacterial and fungal community succession.The main results are as follows:The pathogen sterilization effects by RSD under different conditions of soil properties,organic materials（molasses,sugar powder,bagasse）and previous crops（leafy vegetables,eggplant fruit,strawberries）were different,so were the physical and chemical properties of soil and the microbial numbers.The more severe the soil acidification,salinization and soil-borne diseases,the greater the changes in soil p H,EC and pathogen number after RSD treatment.Compared with leaf vegetables and strawberry,RSD treatment in the soil previously planted with fruit crops had more significant effect on soil physical and chemical properties,and had better control effect on Fusarium oxysporum.RSD treatment of bagasse had the highest inhibition rate to F.oxysporum,and RSD treatment of molasses had the best inhibitory effect on F.solani.In the greenhouse conditions,taking the continuous cropping diseased soil as the research object,adding molasses as the organic material to carry out RSD treatment,and continuously planting two season crops after the treatment.The soil physical and chemical characteristics at three time points after RSD treatment,the first and the second crop seasons were analyzed.In this study,the p H of RSD treated soil showed a decreasing trend with crop planting,while the EC and content of nitrate nitrogen increased,indicating that the soil had the tendency of acidification and salinization in the process of crop replantation.In the first season,the number of fungi increased,while in the second season,the number of bacteria and fungi decreased significantly.F.oxysporum and F.solani showed an upward trend in the process of crop cultivation,and the increase amplitude in RSD treatment was higher than that in CK treatment.The dynamic changes of soil microbial community structure and the response of key microbial groups to soil environmental factors were analyzed by quantitative PCR and high-throughput sequencing.The results showed that the diversity index of soil fungal community in RSD treatment was significantly lower than that in CK treatment.After planting tomato in the second season,the richness index of fungi in RSD treatment was further decreased,but there was no significant difference between RSD treatment and CK treatment.Treatment and cultivation had significant effects on soil bacterial community structure.Treatment,cultivation and their interaction had significant effects on soil fungal diversity index and community structure.Further analysis showed that RSD treatment could significantly increase the abundance of functional microorganisms.Many microbial groups in the bacterial community had the ability of disease resistance,phosphorus solubilization or nitrogen fixation,while some species in the fungal community could inhibit other fungi.Along with the two seasons planting,there were 27 biomarker species in the bacterial community of RSD treated soil at different cultivation time.After replanting,the biomarkers contained Solibacterales,Acidobacteriaceae＿Subgroup＿1,Achromobacter,Flavobacterium and Alcaligenaceae.There were 21 biomarker species in the fungal community.The soil biomarkers after crop replantation mainly included Onygenales,Mortierellales,Eurotiales,Hypocreales and Mucorales.Further studies on the relationships between soil microbial community and environmental factors showed that p H,NH₄⁺-N and AP were the strongest predictors of theαandβdiversity of bacterial communities under different treatments.NH₄⁺-N,NO₃^--N,AP and AK contributed the most to explaining the relative abundance of most dominant bacterial communities in different cultivation periods.p H,NH₄⁺-N,and AK were the negative predictors of the relative abundance differences in soil fungal communities and dominant flora under different treatments,while p H,NO₃^--N and NH₄⁺-N contributed the most to the variation of relative abundance of most dominant flora in soil fungal community under different cultivation periods.Co-occurence network analysis showed that the number of nodes and edges,average degree,average path length,and clustering coefficient of the bacterial network in RSD treatment were larger than those in CK treatment.The average degree and clustering coefficient of the fungal network in RSD treatment were larger than those in CK treatment.In conclusion,the initial soil properties,the types of organic materials and the types of preceding crops all affected the effect of RSD treatment.The more serious the continuous cropping obstacle was,the greater the improvement effet of RSD treatment was.After replanting of two seasons crops,the abiotic and biotic properties improved by RSD treatment degraded again.However,the situation of soil physicochemical properties,the pathogens and beneficial microbes in the RSD-treated soil was still better than the untreated soil.The results showed that RSD treatment had a long-term effect on the improvement of degraded soil in greenhouse.