Effects of metam sodium fumigation on the abundance, activity, and diversity of soil bacterial communities

Metam sodium is a fumigant used as a crop pretreatment in agriculture to control a wide array of pests, and soil borne diseases that may adversely affect plant quantity and quality. This present study utilized control and treated field plots to examine the effects of metam sodium on indigenous soil microbes in terms of numbers, activity, and diversity. Following metam sodium application, culturable heterotrophic counts in all soils increased significantly for 24 h, but quickly returned back to original levels. Application resulted in decreased microbial activity, detected by ATP-based assays, that was significantly lower in treated soils than control plots, but recovered quickly. High-throughput sequencing of the 16S rRNA gene showed that treated plots contained significantly lower numbers of observed OTUs, particularly 14, 21, and 28 days after treatment. Soil bacterial communities were significantly altered by MS-treatment due to increased relative abundances of Actinomycetales, Bacilli, and Chloroflexi, as well as decreased Acidobacteria. These dominant taxa observed in MS-treated plots are major contributors to biological activity in various healthy soils and rhizospheres. Therefore, the increase in relative abundance of these biologically productive phyla coupled with abundant ATP production suggests that soil health recovered following MS-treatment and remained functionally intact.