The effects of different arbuscular mycorrhizal fungal agents on nutrient elements in Dianzhong lou and soil
The rhizosphere soil, as the direct substrate for plant growth, provides a guarantee for the growth and development of plants. The microbial composition and enzyme activity in the soil affect the soil microbial ecosystem, and have important impacts on soil physical and chemical properties, nutrient cycling, and plant growth. The soil microbial community plays a crucial role in regulating soil material cycling and improving soil quality. Arbuscular mycorrhizal (AM) fungi can improve soil nutrient composition, promote plant nutrient absorption and utilization, increase the yield and quality of medicinal plants, and play a positive role in ecological restoration of polluted and saline alkali soils.

The depletion of wild Dianzhong Lou resources has made artificial cultivation and introduced cultivation the mainstream of Dianzhong Lou research. However, due to its geographical location and differences in planting years, the quality of Dianzhonglou varies. According to reports, inoculation with different AM fungi can increase the content of dioscin in Dianzhong Lou, improve the physical and chemical properties of soil, enhance soil nutrients, optimize microbial structure, promote chlorophyll synthesis in Dianzhong Lou seedling leaves, and enhance the photosynthetic capacity of seedlings. Zhang et al. reported that inoculating Ambispora leptospiricha and Archaeospora trappei during the symbiotic germination of Dianzhong Lou seeds can improve the survival rate and yield of Dianzhong Lou seedlings. In addition, inoculation with different AM fungi can promote the absorption and utilization of soil nutrients by the rhizosphere of Dianzhong lou and improve its quality. Yang et al. found that inoculating with a preferred mixed AM fungal agent increased the endogenous hormone content in the roots of Dianzhong Lou more effectively than inoculating with a single plant of fungi. Previous studies have found that different AM fungal mixtures can increase the content and enzyme activity of arbuscular mycorrhizal fungi in rhizosphere soil, change the microbial community structure, thereby improving the soil environment. They can also promote the stress resistance of Dianzhong Lou to adverse external environments, increase the total saponin content of Dianzhong Lou, induce changes in secondary metabolism of Dianzhong Lou, increase effective ingredients, and thus enhance the medicinal quality of Dianzhong Lou.

Improving soil environment and enhancing the quality of medicinal herbs through inoculation with AM fungi has become a trend. The level of nutrient element content in soil is influenced by the nutrient level of cultivated soil and the plant’s own habits. Shen et al. found that inoculation with different AM fungi resulted in higher levels of calcium, magnesium, sodium, and other nutrients in the rhizomes and rhizosphere soil of Dianzhong grandiflorus compared to the untreated group, and promoted the absorption of these elements by the rhizomes to improve their quality. Gu et al.’s study showed that mixed inoculation of different AM fungi can increase the absorption of nutrients by wood fragrance, promote the accumulation of metabolites, and improve the yield and medicinal quality of internal lipids in wood fragrance. However, there is limited research on the effects of inoculation with different AM fungal mixtures on nutrient elements in Dianzhong Lou and soil microecology. Based on this, this study determined the content of nutrients in different parts of Dianzhong Lou and soil by inoculating different combinations of AM fungal agents, aiming to analyze the effects of different AM fungal agents on nutrients in Dianzhong Lou and soil, in order to maximize the utilization of soil nutrients, reduce resource waste, and lay a theoretical foundation for the development of Dianzhong Lou bio fertilizers.

 

Inoculation with different AM fungal agents can affect to varying degrees the absorption and accumulation of nutrients in Dianzhong Lou and cultivated soil. Nitrogen, phosphorus, and potassium are essential elements for plant growth and development, and their distribution in the body can reflect the distribution and interaction of elements in plants. After inoculation with different combinations of AM fungal agents, the content of different elements showed dynamic changes at different growth stages. Among them, the S8 treatment group showed an increase in nitrogen content in new and old roots and leaves at T1 stage, new roots and leaves at T2 stage, and new and old roots and leaves at T4 stage; The phosphorus content in the new rhizomes of the S8 treatment group during the T1 period increased (up to 6.289g/kg), suggesting that the AM fungi in the S8 treatment group can promote the absorption of nitrogen and phosphorus elements from the soil to improve yield and quality of Dianzhong. Consistent with Li et al.’s research, increasing the application of nitrogen and phosphorus fertilizers can increase the yield and saponin content of Dianzhonglou. The potassium content in the old roots and stems of the S8 treatment group during the T4 period was relatively high, at 12.715g/kg; Moreover, Wang et al. reported that potassium in the soil is beneficial for the synthesis and accumulation of total saponins and polysaccharides in the rhizomes of Dianthus chinensis, and its impact may be achieved through the potassium content in different parts of Dianthus chinensis. The calcium content of stems and leaves during T1 and T3 stages, as well as new and old roots and stems during T4 stage, increased in the S8 treatment group; The magnesium content in the new rhizomes increased during T1, T2, and T4 periods (up to 28.142 g/kg). Calcium is not only an important component of plant cell walls and membranes, but also can effectively alleviate various biotic and abiotic threats to plants, improve plant stress resistance, and play an important role in growth, development, maturation, and aging.

The quality of medicinal plants can indirectly reflect soil quality and fertility, and changes in the microecology of rhizosphere soil can also affect the quality of medicinal plants. The content of AM fungi and other microorganisms can cause changes in soil matrix environment and have a significant impact on the composition and structure of microbial communities. This study found that, except for the significant increase in nitrogen content in the new and old rhizomes and leaves of Dianzhong Lou in the S6 and S8 treatment groups, and the higher phosphorus content in the new rhizomes of Dianzhong Lou in the S8 and S1 treatment groups compared to other treatment groups (up to 6.289g/kg), the changes in nitrogen, phosphorus, potassium, and magnesium elements in the soil of different treatment groups were not significant. There was a significant increase in calcium content in the soil of different treatment groups, especially in the S8 treatment group where the calcium content was significantly higher than that of the control group. Therefore, inoculation with a mixture of different arbuscular mycorrhizal fungi can effectively alter the nitrogen, phosphorus, potassium, calcium, and magnesium content in different parts of Dianzhong Lou medicinal herbs, promoting the absorption of nutrients by Dianzhong Lou. At the same time, it can also alter the release of nutrients in the soil, which is consistent with the study of the advantageous role of AM mycorrhizal fungi in nutrient competition.

Correlation analysis shows that the absorption of N in the old roots and stems of Dianzhong Building is significantly correlated with the absorption of Ca and Mg, the absorption of N in the new roots and stems is significantly correlated with the absorption of P and Mg, the absorption of P and K, the absorption of N in leaves and the absorption of K in stems are significantly synergistic with the absorption of Ca, and the absorption of Ca in the old roots and stems is significantly negatively correlated with the absorption of Ca and Mg in the soil. The absorption of K in stems is negatively correlated with the absorption of P in the soil, and the absorption of Mg in stems is negatively correlated with the absorption of Mg in the soil. The accumulation of multiple nutrients during the growth process of Dianzhong Tower, as speculated by Zhang et al., may have both competitive and synergistic effects. There is a synergistic effect between the absorption of nitrogen, calcium, and magnesium in the old roots of Dianzhong Lou. The phosphorus content in Dianzhong Lou leaves increases with the increase of soil calcium content, and there is a complex interaction between calcium and phosphorus with species specificity. High calcium can increase the absorption of phosphorus by leguminous plants but inhibit the absorption of phosphorus by wheat, tomatoes, and other plants.

In summary, the six AM fungi in the S8 treatment group, namely G. albida, G. gigantea, S. calospora, R. fulgida, R. intraradii, and C. claroideum, are excellent strains for the development of Yunnan Chonglou bio fertilizers, laying the foundation for the research and development of bio fertilizers. The results of this study showed that the combination of 9 different AM fungal agents can affect the transfer and accumulation of nutrient elements to varying degrees. However, in order to screen for the optimal mixed agent, further experiments are needed to verify its inoculation ratio and the composition of the fermentation broth, in order to lay a theoretical foundation for the development and application of bio fertilizers in Dianzhong Lou, and to facilitate the change of nutrient absorption and accumulation in Dianzhong Lou, and improve its quality.