Abstract
Chloropicrin (CP) can effectively combat soil-borne diseases but has significant side effects on nontarget microorganisms. The rhizosphere microflora play a crucial role in promoting plant growth and protecting plants from infection by soil-borne pathogens. We conducted a laboratory pot experiment to evaluate the effect of CP on the rhizosphere soil bacterial flora and the effect of biochar amendments on the reconstruction of microbial communities. Our results show that CP fumigation and biochar additions promoted the growth of cucumber plants in the later stage of the pot experiment. CP significantly inhibited the rhizobacterial diversity and changed the community composition. Biochar amendments after CP fumigation shortened the time for the rhizobacterial diversity to recover to unfumigated levels. Biochar amendments promoted the transplantation of new populations to empty microbiome niches that were caused by CP and, in particular, stimulated many beneficial microorganisms to become the predominant flora. The relative abundances of many functional taxa related to plant-disease suppressiveness and pollutant bioremediation increased, including Pseudomonas, Stenotrophomonas, Bacillus, Massilia, Acinetobacter, Delftia, Micromonospora, Cytophagaceae, and Flavisolibacter. These changes stimulated by biochar amendments would promote multifunctionality in the soil rhizosphere and benefit plant growth and disease resistance.
Highlights
In the 60-day samples, the stems of the cucumber seedlings in the soil treated with high-dosage CP fumigation and biochar amendments were significantly thicker than those of the control
The results indicate that biochar additions benefit the restoration of rhizobacterial diversity and shorten the time for the diversity to recover to a level similar to that of the control, when microbial abundances are at a low level
The change of root zone environment, in conjunction with a reduction in soil acidity and the selectivity of biochar, is probably responsible for the change of the predominant members of the rhizobacterial communities in biochar-amended soils following CP fumigation. This is the first study that reports the responses of rhizosphere soil microbial communities to biochar amendments after CP fumigation
Summary
Soil fumigation is recognized as an effective method to combat soil-borne diseases. As a fumigant with the broadest range of applications, methyl bromide (MB) has an excellent control effect on soil-borne pathogens, pests, and weeds [1]. Under the provisions of the Montreal Protocol, developing countries were required to phase out controlled uses of MB by 1 January 2015 because of its ozone-depleting properties [2]. As one of the substitutes for MB, chloropicrin (CP) can provide broad-spectrum and effective control of soil-borne pathogenic bacteria, fungi, nematodes, and weeds, such as Ralstonia solanacarum, Verticillium dahlia, Fusarium oxysporum, Meloidogyne, and Cyperus rotundus L. In China, approximately 10,000 tons of CP are produced every year for pre-plant soil fumigation (official data from the Ministry of Agriculture and Rural Affairs of China in 2017)
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