Application of cellulose-rich organic resource improves soil quality and plant growth by recruiting beneficial microorganisms

Organic amendments are commonly used to suppress soil-borne diseases by modulating the soil microbial community. However, it remains unclear whether organic amendments have universal suppression mechanisms across different soil resident microbiomes. Here, we established diseased (D) and healthy (H) microbiomes to examine the impacts of alfalfa and carboxymethylcellulose amendments on soil microbial communities, soil-borne pathogen suppression, and plant growth promotion. Our results indicated that both organic amendments significantly decreased the relative abundance of Fusarium, modified the soil physicochemical properties and microbial community in both diseased and healthy soils. Specifically, organic amendment significantly increased soil microbial activity, stimulated the growth of copiotrophic and plant-growth-promoting microorganisms. The application of carboxymethylcellulose resulted in a greater degree of pathogen control than the application of alfalfa straw, leading to the lowest pathogen abundance and disease severity index in watermelon. Organic amendment did not prevent Fusarium wilt outbreaks in diseased soil but significantly increased dry weight of watermelon in healthy soil. Additionally, the same organic amendment recruited the same specific biomarkers in different soil systems, and we found that cellulose was responsible for proliferation of pathogen-suppressive biomarkers (PSBs). These microbial changes contributed to positive effects on pathogen resilience and watermelon growth under cellulose-rich organic amendment. The in vitro tests further revealed that most bacterial PSB strains (i.e. Chitinophaga, Pseudoxanthomonas, Rhizobium, Ensifer, and Luteimonas) exhibited antagonistic activities against F. oxysporum and had a beneficial impact on plant growth. Overall, this study provides significant insights into the response of soil microbiome to organic amendment, and emphasizes the importance of beneficial biomarkers associated with cellulose-rich organic resources for soil quality and plant growth.