Effects of Different Microbial Inoculants and Their Combinations on the Growth and Quality of Stem Lettuce

Purpose To explore the effects of different microbial inoculants and their combinations on the growth, nutrient accumulation, and quality of lettuce (Lactuca sativa L. var. angustata), and to screen for optimal microbial consortia, thereby providing a theoretical basis for the development of compound microbial fertilizers for lettuce.

Methods A pot experiment was conducted with eight treatments: no-inoculant control (CK), Bacillus amyloliquefaciens (T₁), B. subtilis (T₂), B. subtilis B9 (T₃), B. amyloliquefaciens+B. subtilis (T₄), B. amyloliquefaciens+ B. subtilis B9 (T₅), B. subtilis+B. subtilis B9 (T₆), and B. amyloliquefaciens+B. subtilis+B. subtilis B9 (T₇). The differences in indicators among different treatments were compared using analysis of variance, and a comprehensive evaluation was conducted using principal component analysis (PCA).

Results Compared with CK, the plant height, stem diameter, above-ground fresh weight of, and above-ground dry matter accumulation of lettuce in the microbial treatments increased by 2.34%-18.80%, 10.44%-39.31%, 5.92%-32.78%, and 4.23%-45.19%, respectively. The above-ground accumulation of nitrogen (N), phosphorus (P), and potassium (K) increased by 1.55%-27.21%, 10.26%-42.74%, and 5.99%-34.06%, respectively. Meanwhile, the contents of soluble protein, soluble sugar, vitamin C (Vc), and free amino acids in the stems increased by 2.05%-28.02%, 20.71%-71.74%, 8.86%-17.16%, and 9.47%-163.00%, respectively; and in the leaves, these parameters increased by 8.57%-68.33%, 15.88%-62.15%, 2.16%-25.12%, and 9.16%-97.52%, respectively. Furthermore, the nitrate content in the stems and leaves decreased by 19.99%-54.20% and 15.65%-26.70%, respectively.

Conclusion The application of microbial inoculants significantly promotes the growth and nutrient accumulation of lettuce, improves its nutritional quality, and reduces nitrate content. PCA shows that the comprehensive scores of the treatments are as follows: T₅>T₇>T₁>T₃>T₆>T₄>T₂>CK, among which the B. amyloliquefaciens+B. subtilis B9 (T₅) treatment exhibits the best overall performance.