Objectives The cultivation of pear container seedlings is a critical technique for establishing efficient pear orchards, reducing the rejuvenation period, and rapidly entering the fruiting phase. This study investigated the effects and mechanisms of Trichoderma bio-organic fertilizer in promoting the growth of pear container seedlings, and explored the relationship between soil microbial community composition and growth indices of roots and shoots, to provide a theoretical basis and technical support for container seedling cultivation.

Methods The experiment utilized a two-year-old early maturing variety ‘Sucui 1’ (Pyrus pyrifolia ‘Sucui 1’) as the test material, including three treatments: 80% original soil + 20% ordinary commercial organic fertilizer (OF, calculated by weight, the same below); 80% original soil + 15% ordinary commercial organic fertilizer + 5% Trichoderma bio-organic fertilizer (5%BF); 80% original soil + 5% ordinary commercial organic fertilizer + 15% Trichoderma bio-organic fertilizer (15%BF). The growth indices of both the roots and shoots, as well as the rhizosphere soil microbial community structure of the pear seedlings, were measured.

Results Compared to the control group (OF), the stem diameter increased by 2.6% and 8.8% and the number of flower buds increased by 40.0% and 46.7% in the 5%BF and 15%BF treatments, respectively. Compared to the OF and 5%BF treatments, the 15% BF treatment increased the total root tip number by 40.5% and 37.7% and the total root length by 47.3% and 51.4%, with the highest proportion of fine roots (<2 mm). Zi-Pi analysis (Zi>2.5 and Pi<0.62) indicated that the core taxa were Actinobacteria and Ascomycota in the microbial co-occurrence network. Moreover, the random forest model further predicted that key species were mainly Actinobacteria, including growth-promoting bacteria with biocontrol functions such as Streptomyces and Actinomarinicola. Linear regression analysis demonstrated a highly significant positive correlation between the abundance of Trichoderma and Actinobacteria.

Conclusions The application of a high proportion of Trichoderma bio-organic fertilizer (15%BF) can significantly improve the stem diameter and root development of ‘Sucui 1’ pear container seedlings, and promote seedling growth and flowering. This is an effective way to quickly cultivate seedlings. In addition to the inherent function of Trichoderma, the 15% BF treatment can also enrich the beneficial bacteria, such as Actinobacteria and Streptomyces, which may also play a synergistic role in promoting growth.