Effects of short-term rotation and Trichoderma application on the soil environment and physiological characteristics of Malus hupehensis Rehd. seedlings under replant conditions

In this study, we explored the effects of short-term rotation and Trichoderma application on the plant biomass, root respiration rate, root protective enzymes of Malus hupehensis Rehd., and soil environment under replant conditions, to provide a basis for the prevention of the apple replant disease (ARD). In 2014, old apple orchard soils were treated by rotating peanut, Allium fistulosum L., fallow, and natural grass, and replanted apple orchard soil was used as the control. The soils of the different treatments were mixed well with Trichoderma at a concentration of 0.5% (w/w), and 6 kg of each treated soil was added to a pot (outer diameter, 27 cm; inner diameter, 23 cm; height, 18 cm). Uniform seedlings of Malus hupehensis Rehd. were transplanted to the pots on April 23, 2015. Two seedlings were planted in each pot, and 30 pots were prepared for each treatment. The samples were collected at the end of August, when there were visible differences in seedling growth among the treatments. The results showed that rotating Allium fistulosum L. mixed with Trichoderma could significantly improve the populations of bacteria and actinomycetes in the soil, which increased by 189.4% and 107.1%, respectively. The biomass of M. hupehensis significantly improved, and plant fresh weight, dry weight, height, and diameter increased by 186.3%, 205.9%, 58.8%, and 33.2%, respectively. In addition, the total fine root length, total fine root surface area, total fine root volume, and fine root tip number increased by 147.2%, 225.9%, 298.5%, and 331.3%, respectively. Compared with the control seedlings, the treated seedlings showed higher respiration rate of the root system, Superoxide Dismutase activity and Peroxidase activity by 131.0%, 46.3%, and 110%, respectively. Analysis of the terminal restriction fragment length polymorphism profiles showed that the treatment of short-term crop rotation and Trichoderma changed the soil fungal community structure; improved the Simpson index of the soil fungal community; and reduced the Shannon index, Pielou index, and Margalef index. The results suggest that short-term rotation of Allium fistulosum L. mixed with Trichoderma could alleviate ARD.