Earthworms Modify the Soil Bacterial Community by Regulating the Soil Carbon, Enzyme Activities, and pH

Earthworms, universal invertebrates in the soil, play an important role in accelerating litter decomposition and recycling elements. Peatlands store 30% of the global soil organic carbon pool but are particularly vulnerable to variations in the water level. As the water level in the peatlands decreased, the abundance of soil fauna increased. However, little is known about the changes in soil properties and bacterial community after earthworms enter peat soil and mediate the relationship between soil bacteria and properties. Peat soil supplemented with plant residues was fed to Metaphire earthworms for 55 and 90 days, and the soil affected by earthworms was collected to sequence the bacterial 16S rRNA genes and determine the soil’s chemical properties. Earthworms significantly decreased the pH and increased the dissolved organic carbon (DOC) on day 55, and decreased the DOC, total organic carbon, and polyphenol oxidase activity on day 90. Earthworms also significantly increased the relative abundance of Bacteroides on day 55, which responded positively to carbohydrate degradation. A Kyoto Encyclopedia of Genes and Genomes pathway analysis revealed that earthworms enriched 11 predicted metabolic functions, including carbohydrate degradation. Moreover, earthworms dramatically improved the correlation between soil bacteria and primarily indirectly affected the bacterial diversity by regulating the soil carbon. Earthworms that enter the peatland cause clear losses of soil carbon and changes in the soil bacterial community, which have a profound impact on element recycling by regulating metabolic functions. This study demonstrates the importance of monitoring the soil fauna in degraded peatlands.