Plant residues regulate intestinal microbial diversity and carbon function of invasive earthworms by increasing the soil carbon content

There are abundant plant residues in peatland soil, whether and how these plant residues influence the composition and structure of earthworm intestinal prokaryotes, as well as the relationship between intestinal prokaryotes and soil physicochemical properties and soil prokaryotes remains elusive. In this view, earthworms were fed with peat soil alone or peat soil supplemented with plant residues for 90 days, after which their intestinal contents and peat soil were collected for 16S rRNA gene sequencing. The findings revealed that Proteobacteria, Actinobacteria and Bacteroidetes dominated the earthworm gut. Plant residues significantly decreased the relative abundance of Chloroflexi while increasing that of Proteobacteria. Meanwhile, plant residues increased the richness, evenness, and diversity of intestinal prokaryotes while decreasing in richness and Shannon diversity shortly afterward. Of note, when plant residues were introduced, soil dissolved organic carbon, total carbon, and extracellular enzyme activity linked with carbon strongly correlated with intestinal prokaryotic community structure. The relative abundance of genes related to cellobiose transport and sugar transporters in earthworm gut was higher than in soil. Over time, the abundance of chitin and starch degradation functional genes in earthworm gut microbes matched that of soil. The structural equation model revealed that plant residues could change the gut microbial diversity and carbon function genes of earthworms by regulating soil carbon content. This study suggested that the practice of removing plant residues in soil research needs to be reconsidered.