Objective Two strains of plant growth-promoting fungi were isolated from Juncao rhizosphere with performance determined in laboratory.

Methods Fungi with high nitrogen-fixing capability for growth of plants were isolated from Juncao rhizosphere soil using the dilution plate method. Physiochemical characteristics and ITS sequences of two highly active strains were used to identify the species. A pot experiment using lettuce was conducted to evaluate the plant growth-promoting effect of the isolated strains.

Results The two strains, Gt-3 and Gt-29, were identified to be Aspergillus niger and Trichoderma longibrachiatum, respectively. They could solubilize potassium, degrade silicates, and produce siderophores, protease, amylase, and cellulase. In addition, Gt-3 also exhibited a phosphate-solubilizing capability. The pot experimentation verified the ability of both strains in promoting the growth of lettuce. The presence of Gt-29 resulted in the increases of 363.5% on weight of fresh lettuce shoots and 29.0% on plant height, while Gt-3 187.2% on shoot weight and 24.2% on plant height over control. Furthermore, the nutritional quality (e.g., soluble sugar, protein, and vitamin C contents) and antioxidant enzyme activities (e.g., POD, SOD, PPO, and CAT) of the lettuce were significantly improved as well.

Conclusion A. niger and T. longibrachiatum isolated from Juncao rhizosphere could promote, in different degrees, the growth, nutritional quality, and antioxidant enzyme activities of the potted lettuce. The two strains varied in siderophore production, extracellular enzyme secretion, and silicate degradation, and A. niger had an additional function of solubilizing phosphate.