Effects of seaweed fertilizer on the growth of Malus hupehensis Rehd. seedlings, soil enzyme activities and fungal communities under replant condition

•The addition of seaweed fertilizer significantly increased the seedlings growth.•The seaweed fertilizer obviously changed the replant soil fungal communities.•The seaweed fertilizer improved the soil enzyme activities in replant soil.•The application of seaweed fertilizer to replant soil can alleviate the ARD.

Seaweed and its derivatives are widely used as nutrient supplements, biofertilizers, and biostimulants for soil in agriculture. The aim of this study was to evaluate the effects of seaweed fertilizer on the growth of apple (Malus hupehensis Rehd.) seedlings under replant conditions. We investigated the growth of apple seedlings in replant soil treated with seaweed fertilizer at application rates of 0, 5, 20, and 40 g kg−1. The addition of seaweed fertilizer significantly increased the plant height and dry weight of apple seedlings. Seedlings grown in soil treated with seaweed fertilizer, particularly the dose of 40 g kg−1 soil showed higher activities of antioxidant enzymes including superoxide dismutase, peroxidase and catalase, which was accompanied by lower malondialdehyde accumulation. The activities of soil enzymes (invertase, urease, proteinase and phosphatase) were higher in soil treated with seaweed fertilizer than in control soil. An analysis of terminal restriction fragment length polymorphism profiles showed that the fungal communities differed markedly between the 40 g kg−1 seaweed fertilizer treatments and the 0, 5, and 20 g kg−1 treatments. The highest values of Shannon diversity index, evenness index and richness index were in the 40 g kg−1 seaweed fertilizer treatments, and the lowest values of these indexes were in the control. These results suggested that seaweed fertilizer application at a dose of 40 g kg−1 can improve soil enzymes activities, change the soil fungal communities, and improve soil quality. These changes can promote seedlings growth, increase antioxidant activity, and decrease lipid peroxidation in roots, thereby alleviating apple replant disease.