Effects of Bacillus subtilis on photosynthesis and yield of pakchoi under magnetoelectric brackish water irrigation

•1Optimal Bacillus subtilis concentration: 30 g/kg enhances pakchoi photosynthesis.•Best photosynthetic model: Non-rectangular hyperbola model fits data best (R² >0.99).•Maximum yield: Achieved at 30 g/kg Bacillus subtilis, 56.57 t/ha.•Increased application rate: 37.62 g/kg Bacillus subtilis yields up to 54.61 t/ha.•Magneto-electric water benefits: Enhances photosynthesis and yield in arid regions. This study aimed to elucidate the effects of magnetoelectric brackish water irrigation and Bacillus subtilis on the photosynthetic characteristics and yield of pakchoi in arid regions, and identify the optimal photosynthetic response model. Pakchoi was used as the subject, with magnetoelectric brackish water as the irrigation source and five different concentrations of Bacillus subtilis treatments (0, 10, 20, 30, and 40 g/kg), totaling six treatment groups. Photosynthetic response curves were measured at maturity, and the response processes were fitted and compared using the rectangular hyperbola model, non-rectangular hyperbola model, exponential model, and the Ye zi-piao model to explore the photosynthetic characteristics, model applicability, and yield changes under different Bacillus subtilis concentrations. Results indicated that the net photosynthetic rate (Pn) of pakchoi was highest under the MB3 treatment. As the Bacillus subtilis application rate increased, the maximum net photosynthetic rate (Pnmax) showed a trend of initially increasing and then decreasing, with 30 g/kg of Bacillus subtilis being the most effective for enhancing Pnmax. Analysis of fit indices such as the coefficient of determination (R²) revealed that the fit of the photosynthetic response models in the southern Xinjiang arid region was in the order: non-rectangular hyperbola model > Ye zi-piao model > exponential model > rectangular hyperbola model, with the non-rectangular hyperbola model providing the best fit, with an R² value greater than 0.99. In this model, parameters including maximum Pnmax, apparent quantum efficiency (α), dark respiration rate (Rd), light saturation point (Isat), and light compensation point (Ic) were optimal at a Bacillus subtilis concentration of 30 g/kg, achieving the highest pakchoi yield of 56.57 t/ha. Analysis using the quadratic regression model indicated that under the experimental conditions, increasing the Bacillus subtilis application rate to 37.62 g/kg could achieve a maximum yield of c t/ha. The results demonstrate that combining magnetoelectric