不同熏蒸剂对草莓连作土壤养分和微生物群落的影响

【背景】草莓连年栽培导致土传病害问题突出，施用熏蒸剂进行土壤消毒因效果显著得以广泛应用。但不同熏蒸剂对土壤病原微生物的影响存在较大差异，同时对非靶标微生物和土壤理化性质也会有不同程度的影响。【目的】明确不同熏蒸剂对草莓连作土壤养分和土壤细菌、真菌群落结构的影响，为合理选择熏蒸剂提供科学依据。【方法】以连作土壤为材料设置5个处理：未熏蒸、石灰氮熏蒸、石灰熏蒸、棉隆熏蒸、威百亩熏蒸，测定熏蒸处理后土壤养分含量；采用PacBio测序平台分析土壤微生物多样性的变化。【结果】石灰氮和威百亩处理均增加了碱解氮含量，降低了有机质、有效磷和速效钾含量；棉隆处理土壤中各养分含量均增加；石灰处理除有机质含量增加外，碱解氮、有效磷和速效钾含量均降低；棉隆、石灰和威百亩处理显著降低pH值。5个处理草莓连作土壤样本中获得了1 164个细菌OTU和444个真菌OTU。细菌多样性和丰富度分析发现，4种熏蒸剂处理均增加了土壤细菌群落的丰富度，石灰氮、石灰和威百亩处理增加了土壤细菌菌落的多样性。4种熏蒸剂处理真菌菌落的丰富度低于对照；石灰、棉隆处理真菌菌落的多样性高于对照和石灰氮、威百亩处理低于对照，但差异不显著。在物种组成分析中，从门水平看，变形菌门(Proteobacteria)和芽单胞菌门(Gemmatimonadetes)为优势细菌门；与对照相比，石灰氮、石灰、棉隆处理变形菌门相对丰度增高，威百亩处理相对丰度降低。4种处理均降低了芽单胞菌门的相对丰度。其他门类中，4种处理均增加了浮霉菌门(Planctomycetota)、疣微菌门(Verrucomicrobia)的相对丰度。优势细菌群落分析表明土壤熏蒸减少了芽单胞菌属(Gemmatimonas)、藤黄单胞菌属(Luteimonas)、中慢生根瘤菌属(Mesorhizobium)等细菌的相对丰度，增加了噬几丁质菌属(Chitinophaga)、苍白杆菌属(Ochrobactrum)的相对丰度。子囊菌门(Ascomycota)为优势真菌，石灰氮、石灰、棉隆、威百亩4种处理均增加了子囊菌门的相对丰度。另外还检测到引起草莓根部土传病害的枝孢属(Cladosporium)和镰刀菌属(Fusarium)病菌，熏蒸处理后均降低了枝孢属和镰刀菌属的相对丰度，其中枝孢属在石灰氮、石灰、棉隆、威百亩处理中分别降低了1.35%、1.11%、0.90%和1.31%，镰刀菌属分别降低了0.71%、0.85%、0.19%和0.65%，但差异不显著。4种土壤熏蒸剂均增加了有益真菌毛壳菌属(Chaetomium)的相对丰度。【结论】采用熏蒸剂处理连作土壤改变了微生物群落构成，减少或灭杀土壤中的大部分致病菌属，起到有效防治草莓土传病害的作用，但不能灭杀所有病菌，而且对有益菌和土壤理化性质有不同程度的影响，因此处理后补充有益微生物非常关键。根据对病原菌的灭杀效果，石灰氮、威百亩处理的效果优于其他处理，可作为轮换施用的熏蒸剂，本试验条件下，棉隆是一种弱的处理剂。

Effects of different fumigants on soil nutrients and microbial communities of strawberry continuous cropping

[Background] The problem of soil-borne diseases caused by successive cultivation of strawberries has become more and more prominent, and fumigants have been widely used for soil disinfection because of their remarkable effect. However, different fumigants have different effects on soil pathogenic organisms, and at the same time, they have different effects on non-target organisms and soil properties. [Objective] To explore the effects of different fumigants on soil nutrients, soil bacteria, and fungal diversity, thereby providing a scientific basis for the reasonable selection of fumigants. [Methods] Continuous cropping soil was used as material and treated with five treatments including control, soil fumigation using calcium cyanamide, soil fumigation using calcium oxide, soil fumigation using dazomet, and soil fumigation using metam-sodium, to measure soil nutrient content after fumigation. PacBio sequencing platform was used to analyze the microbial diversity of soil. [Results] Both calcium cyanamide and metam-sodium treatments increased the content of alkali-hydrolyzable nitrogen and decreased the content of organic matter, available phosphorus, and available potassium. Each nutrient content in the soil of dazomet treatment increased, while the content of alkali-hydrolyzable nitrogen, available phosphorus, and available potassium in calcium oxide treatment decreased except the content of organic matter. In addition, the pH of dazomet, calcium oxide, and metam-sodium treatments decreased significantly. A total of 1 164 bacterial OTUs and 444 fungal OTUs were obtained from five soil samples of strawberry continuous cropping. Analysis of bacterial diversity and richness showed that four fumigant treatments increased the richness of the soil bacterial community, and calcium cyanamide, calcium oxide, and metam-sodium treatments increased the diversity of soil bacterial colonies. As compared with the control, the richness of fungal colonies treated with four fumigants was lower, and the diversity of fungal colonies in calcium oxide and dazomet treatments was higher while that in calcium cyanamide and metam-sodium treatments was lower, but the difference was not significant. In the analysis of species composition, from the phylum level, the dominant bacterial phyla were Proteobacteria and Gemmatimonadetes. As compared with control, the relative abundance of Proteobacteria in calcium cyanamide, calcium oxide, and dazomet treatments increased, while that in metam-sodium treatments decreased. All four treatments reduced the relative abundance of Gemmatimonadetes. The four soil fumigation treatments increased the relative abundance of Planctomycetota and Verrucomicrobia in other phyla. The analysis of dominant bacterial communities showed that soil fumigation reduced the relative abundance of bacteria such as Gemmatimonas, Luteimonas, and Mesorhizobium, but increased that of Chitinophaga and Ochrobactrum. The dominant fungus phylum was Ascomycota, and the relative abundance of Ascomycota was increased by calcium cyanamide, calcium oxide, dazomet, and metam-sodium treatments. Cladosporium and Fusarium causing soil-borne diseases in strawberry roots were detected, and the relative abundance of Cladosporium and Fusarium decreased after the fumigant treatment, among which Cladosporium decreased by 1.35%, 1.11%, 0.90%, and 1.31%, and Fusarium decreased by 0.71%, 0.85%, 0.19%, and 0.65% in calcium cyanamide, calcium oxide, dazomet, and metam-sodium treatments, respectively. All four soil fumigants increased the relative abundance of Chaetomium, a beneficial fungus. [Conclusion] Comprehensive analysis shows that fumigant treatment of continuous cropping soil changes the microbial community composition, and reduces or kills most pathogenic bacteria in the soil, thus playing an effective role in preventing and controlling soil-borne diseases of strawberries. However, it cannot kill all pathogens and affect beneficial bacteria and soil properties to different degrees. Therefore, it is very important to supplement beneficial microorganisms after treatment. According to the killing effect of pathogenic bacteria, calcium cyanamide and metam-sodium treatments are superior to other treatments and can be used as fumigants for soil application in turn. Under this experimental condition, dazomet is a weak treatment agent.