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

Abstract:

[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.

Key words:strawberry;fumigants;soil microbial community;diversity