Relationships of decomposability and C/N ratio in different types of organic matter with suppression of Fusarium oxysporum and microbial communities during reductive soil disinfestation

• The decomposability of plant residuals was positively related to DE of RSD.
• C/N of plant residuals had a significant negative correlation with DE of RSD.
• Clarifying the changes of dominant bacteria during RSD and their main functions.

Although reductive soil disinfestation (RSD) is an effective method for suppressing Fusarium oxysporum, there is limited information on the relationships among types of organic matter, disinfestation efficiencies (DEs), and changes in soil functional microorganisms during the RSD process. Hence, we performed laboratory experiments using nine different organic materials and used quantitative real-time PCR and MiSeq pyrosequencing to investigate the suppression of F. oxysporum and changes in soil microbial communities during the RSD process. The results showed that the RSD treatments using different organic matters significantly decreased F. oxysporum populations in the soil, but DEs of the RSD treatments were dramatically different. Contents of easily oxidized organic carbon (EOC) in these plant residuals (sugarcane leaf, banana leaf, alfalfa, rice husk, wheat bran, reed, and sugarcane residue) had a significant positive correlation with the DEs and that in all of the organic matters had a significant positive correlation with total organic acid contents. The C/N values of these plant residuals had a significant negative correlation with DEs. Furthermore, the soil bacterial community during the alfalfa RSD process was significantly changed. In the early stage of the RSD treatment, relative abundances of Coprococcus (Firmicutes), UC-Clostridiaceae (Firmicutes), and Klebsiella (Proteobacteria) increased significantly and had a significant positive correlation with organic acids. In contrast, relative abundances of UC-Cytophagaceae (Bacteroidetes) and UC-Xanthomonadaceae (Proteobacteria) decreased significantly. In the later stage of the RSD treatment, the number of Opitutus (Verrucomicrobia) and UC-Clostridiales (Firmicutes) increased significantly. During the entire RSD process, relative abundances of decomposers of less-degradable organic carbon, such as UC-Chitinophagaceae (Bacteroidetes), Clostridium (Firmicutes), UC-Ruminococcaceae (Firmicutes), Pseudoxanthomonas (Proteobacteria), and Flavisolibacter (Bacteroidetes), were always higher than their initial relative abundance values. Overall, types of organic matter with lower C/N could induce higher DEs; organic matters with higher EOC could stimulate organic acid producers to produce more toxic organic acids and consequently induce higher DEs during the RSD process. Dominant functional microorganisms found during the alfalfa RSD treatment belonged to Firmicutes, Proteobacteria, and Bacteroidetes.