The impact of microbial fertilizer Bacillus velezensis GB03 on photosynthetic characteristics and yield of Pinot Noir grape plants under salt stress

Grape is a major economic crop in northwestern China, playing a vital role in the region's agricultural economy. However, in recent years, soil salinization has intensified due to global warming and improper irrigation practices, resulting in significant declines in grape yield and quality. Addressing the adverse effects of salt stress on grape growth is of critical importance. Therefore, this study explored the effects of the exogenous application of microbial fertilizer Bacillus velezensis GB03 on the photosynthesis of Pinot Noir grapes under salt stress. Using Pinot Noir plants under normal growth conditions as the control group, salt stress was simulated by applying 200 mM NaCl. The microbial fertilizer GB03 was first diluted with water and then applied exogenously at three concentrations: low (300-fold dilution), medium (200-fold dilution), and high (100-fold dilution). The study measured the effects of these treatments on photosynthetic gas exchange parameters, chlorophyll fluorescence parameters, relative chlorophyll content, and single-plant yield under salt stress. The results demonstrated that salt stress significantly reduced photosynthesis in grape leaves, whereas the application of microbial fertilizer notably enhanced photosynthetic efficiency and fruit yield. Among the treatments, the medium-concentration fertilizer group exhibited the most pronounced improvements in net photosynthetic rate (A), transpiration rate (E), stomatal conductance (gs), and single-plant yield (SPY). Furthermore, chlorophyll fluorescence parameters and relative chlorophyll content in this group were significantly higher than those in the other treatment groups. Principal component analysis confirmed that the medium-concentration treatment had the highest photosynthetic capacity, suggesting that it effectively alleviated salt stress by enhancing photosynthetic performance, thereby increasing fruit yield. This study provides a scientific foundation for the use of microbial fertilizers to mitigate soil salinization and improve salt tolerance in grape cultivation. The findings have significant implications for enhancing grape yield and quality under saline conditions.