Effects of different microbial fertilizers on the growth and development of pomegranate seedlings

【Objective】Pomegranate (Punica granatum L.) is highly valued for its nutritional and cultural significance. However, its production is often constrained by soil quality issues, such as soil desertification, which can result in reduced yield, leaf chlorosis, and smaller arils. To mitigate these impacts, increased water and fertilizer inputs are commonly employed in pomegranate seedling cultivation. However, the excessive application of chemical fertilizers is one of the main causes of soil salinization and alkalinization. Microbial fertilizers, a specialized bio- formulation containing beneficial microbial strains, enhance nutrient uptake efficiency and suppress soil-borne diseases. Additionally, they improve soil quality by activating organic matter and increasing soil enzyme activity, thereby supporting sustainable soil development. This study compared the effects of different types of microbial fertilizers on seedling growth and soil quality, identifying the most effective fertilizer for promoting pomegranate seedling development.【Methods】Two-year-old cuttings of Huaguan cultivar (P. granatum L.) from the National Horticultural Germplasm Repository (Zhengzhou) were used as experimental materials. A control group (CK) without microbial fertilizer was established, alongside five microbial fertilizer treatments: Vigorous Source (T1, incorporation), Trichoderma harzianum (T2, fertigation), microbial inoculant (powder form, T3, incorporation), microbial inoculant (granular form, T4, incorporation), and soil activator (T5, fertigation). Each treatment consisted of 10 replicates. The effects of different microbial fertilizer on the growth and development of seedlings were studied. Plant height, stem diameter, and the number of new shoots were measured on each seedling under each treatment. After leaf shedding, the fresh weight of the plants was measured with three biological replicates for each treatment. Fresh leaves were collected from each treatment to measure chlorophyll a, chlorophyll b, carotenoid, and total chlorophyll contents, with three biological replicates for each measurement. Fully expanded leaves from each treatment were selected to determine photosynthetic parameters, including net photosynthetic rate (Pn), transpiration rate (Tr), stomatal conductance (Gs), intercellular CO2 concentration (Ci), and water use efficiency (WUE). Each measurement included three biological replicates and two technical replicates. After leaf shedding, the pH of different treated substrates was measured with three biological replicates for each treatment. The experimental results provided a comprehensive evaluation of seedling growth and photosynthetic performance under different microbial fertilizer treatments.【Results】We revealed that the application of microbial fertilizers significantly affected the growth and development of seedlings, with the T1 demonstrating the most pronounced effects. In June, the plant height of seedlings with T1 and T3 was significantly higher than that of CK, with increases of 25.82% and 15.89%, respectively. Stem diameter with T1, T2, T3, and T4 was higher than CK, and the number of new shoots increased across all treatments compared to CK. In July, there were no significant differences in plant height among treatments, but the stem diameter with T1, T2, and T3 was significantly higher than CK, with increases of 69.06%, 30.94%, and 43.17%, respectively. The number of new shoots with T1 was significantly higher than CK, with an increase of 46.88%. Leaf chlorophyll a, chlorophyll b, carotenoid, and total chlorophyll contents increased across all treatments compared to CK. Chlorophyll a and total chlorophyll contents were significantly higher in all treatments, with T1 showing the highest values. Photosynthetic parameters (Pn, Tr, Gs, Ci, and WUE) were also influenced by microbial fertilizer application. In the T1, Gs at 8:00 was significantly higher than CK, with no significant reductions at other time points. Ci at 14:00 was significantly lower than CK, with no significant increases at other time points. WUE at 14:00 was significantly higher than CK at the 0.05 level, with no significant reductions at other time points.【Conclusion】Different microbial fertilizer treatments had varying effects on the growth and development of P. granatum L. seedlings. The efficacy of these treatments was significantly influenced by the active components and microbial strains in the fertilizer. Vigorous Source was identified as the optimal microbial fertilizer, demonstrating the most significant promotion of plant height, stem diameter, number of new shoots, chlorophyll content, and photosynthetic efficiency during the growth and development stages. The application of Vigorous Source can accelerate the cultivation of high-quality pomegranate seedlings through a well-optimized fertilization strategy.