Effect of fumigation with chloropicrin on soil bacterial communities and genes encoding key enzymes involved in nitrogen cycling.

Chloropicrin (CP) is a potential alternative for methyl bromide as a soil fumigant given that the use of methyl bromide has become limited. However, little is known about how fumigation with CP affects the condition of the soil microbial community. In this study, 16S rRNA amplicon sequencing and quantitative PCR were combined to investigate the effect of CP on soil bacterial community. In total, 938,922 effective reads were obtained from 18 samples and clustered into 58,662 operational taxonomic units at a similarity cut-off of 97%. Both approaches showed that the primary structure of bacterial community in soil did not significantly change at the phylum level after fumigation, but CP had a significant impact on the abundance of the bacterial microbiome that was recovered and identified. Additionally, bacterial community diversity decreased significantly, and there was a shift in the predominant populations. Staphylococcus, Actinomadura, Acinetobacter and Streptomyces significantly decreased in number or disappeared, and Bacteroides, Lachnoclostridium, Pseudoalteromonas, Colwellia, Idiomarina and Cobetia became the new predominant populations. In addition, some species associated with biodegradation, such as Sphingomonas spp. and Rhodococcus spp., significantly increased in number. The abundance of ammonia-oxidizing archaea (AOA) were significantly inhibited, yet the abundance of ammonia-oxidizing bacteria (AOB) significantly increased, and denitrification was significantly promoted. These changes in bacterial flora can considerably impact soil function and health and lead to negative effects on the environment surrounding fumigated soils, indicating the need for proactive risk management. Our study provides useful information for environmental safety assessments of CP in China.