Chemical fumigation combined with soil amendments of contrasting carbon availability alters soil bacterial and fungal community diversity

Chemical fumigation is used to reduce soil-borne diseases in agricultural production systems; however, non -targeted soil microorganisms may also be affected. This study investigated the effects of chemical fumigation and substrate carbon (C) availability on the soil bacterial and fungal community diversity under controlled conditions over 128 days. This study consisted of a 3 x 3 factorial arrangement of three fumigant treatments (fumigation with chloropicrin [CP], metam sodium [MS], or no fumigation) and three soil amendment treat-ments (amendment with young barley, mature barley, or no amendment). MS fumigation transiently decreased bacterial species evenness when combined with young barley residues; however, it did not affect fungal diversity indices. CP fumigation, regardless of soil amendment or substrate C availability, decreased bacterial species evenness and richness that did not recover over time. However, CP fumigation only decreased fungal species evenness and richness when combined with young or mature barley residues. Although all treatments resulted in a bacterial and fungal community that was significantly dissimilar to the non-fumigated unamended soil, CP fumigated soils had the most dissimilar bacterial and fungal 0-diversity after 128 days. This study demonstrated that the addition of young or mature barley residues to chemically fumigated soil did not recover microbial diversity. Instead, the addition of plant residues to chemically fumigated soil had a greater impact on microbial diversity and community composition compared to chemical fumigation used alone, subsequently promoting a less diverse and selective community for both fumigation and organic C additions.