Objectives We studied the effects of fertilizer forms and soil conditions on apple replant soil disease by using Trichoderma fertilizer to provide effective theoretical basis and technical support for alleviating apple replant disease.
Methods This experiment, using apple rootstock (Malus hupehensis Rehd.) seedlings as the test material, involved four treatments: replant soil (CK), ammonium persulfate (T1), ammonium persulfate plus granular Trichoderma fertilizer (T2), and ammonium persulfate plus powdery Trichoderma fertilizer (T3). Through high-throughput sequencing of soil microorganisms, quantitative real-time PCR and other technologies, the effects of each treatment on soil microbial community structure and number of soil harmful fungi were studied. Physiological characteristics of Malus hupehensis Rehd. seedlings (plant biomass, root respiration rate, and root protective enzyme activity) were determined.
Results Granular and powdery Trichoderma fertilizers promoted the growth of Malus hupehensis Rehd. seedlings in different degrees, improved soil microbial environment, and increased the activities of root protection enzymes and soil enzymes. The promotion effect of granular fertilizer was better than that of powdery fertilizer. Compared with control, T1 treatment significantly improved the growth of M. hupehensis Rehd. seedlings, while T2 and T3 treatments showed significantly higher promoting effects than T1 did. Compared with CK, T1 significantly decreased the activities of sucrase, phosphatase, catalase and urease, while T2 increased those by 45.41%, 92.85%, 56.32% and 186.67%, T3 increased those by 32.96%, 83.89%, 43.68% and 165.56%, respectively. The root activity and root oxidase activity of M. hupehensis Rehd. seedlings were in order of T2 > T3 > T1 > CK, those in T2 treatment were 1.41 and 2.80 times respectively higher than those in CK. Real-time fluorescence quantitative results showed that both ammonium persulfate and Trichoderma fertilizer application could optimize soil microbial environment, increase the number of soil bacteria, and reduce the number of soil harmful fungus (Fusarium solani). Compared with CK, the number of soil bacteria was 2.18 and 2.55 times of hat in CK under T2 and T3 treatment, and the number of soil actinomycetes was 1.71 and 1.53 times under T2 and T3, respectively. Soil high-throughput sequencing data showed that T2 significantly increased the relative abundance of Trichoderma by 58.8%, decreased the relative abundance of Alternaria by 92.87%, while T3 decreased the relative abundance of Fusarium by 64.18%.
Conclusions Ammonium persulfate plus Trichoderma fertilizer could significantly reduce the number of harmful soil fungi, increase the number of soil bacteria, optimize the soil microbial environment, and promote the root activities and growth of M. hupehensis Rehd. seedlings. The effect of ammonium persulfate plus with granular Trichoderma fertilizer is better than that of ammonium persulfate plus powder Trichoderma fertilizer.
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