Molecular Soil Biology 2025, Vol.16, No.1, 45-54 http://bioscipublisher.com/index.php/msb 46 2 Rhizosphere Microorganisms and Their Role in the Growth of Anoectochilus 2.1 Definition and classification of rhizosphere microorganisms The soil area surrounding plant roots is called the rhizosphere, home to a large number of microorganisms, such as bacteria, fungi, and actinomycetes. These microorganisms help plants absorb nutrients, grow efficiently, and reduce disease. Bacillus subtilis and certain actinomycetes not only promote plant growth but also inhibit soil-borne pathogens (Dong et al., 2018; Ning et al., 2020). Among fungi, arbuscular mycorrhizal fungi (AMF) and species from the Mortierella group can help plants absorb more nutrients and make them more resistant to drought or disease (Ning et al., 2020; Sun et al., 2022). Actinomycetes are long, thread-like bacteria that break down organic matter and release substances that fight germs (Wang et al., 2022). Different environments and plant varieties will affect the composition of rhizosphere microorganisms. In the rhizosphere of Anoectochilus roxburghii, with the growth process, the species of bacteria will decrease, while the number of fungi will increase (Dong et al., 2018). This change is related to the amount of nutrients in soil, substances secreted by plant roots, and planting methods such as fertilization and shading (Sun et al., 2022; 2023; Wang et al., 2022). 2.2 The relationship between rhizosphere microorganisms and A. roxburghii and their impact on plant health Rhizosphere microorganisms can interact with Anoectochilus roxburghii, which is very helpful for plant growth. AMF can form a symbiotic relationship with Anoectochilus roxburghii roots, especially when the soil is deficient in phosphorus, it can help it absorb more nutrients, promote root development, and make plants grow better during continuous cultivation (Ning et al., 2020). Beneficial bacteria such as Bacillus subtilis can inhibit the activities of pathogenic fungi such as Fusarium, reduce disease occurrence and improve plant survival rate (Dong et al., 2018; Dong and Li, 2024). When AMF is applied as a biofertilizer, it increases the population of helpful microbes, improves nutrient availability, and lowers the risk of pathogen outbreaks (Ning et al., 2020). Root exudates fromA. roxburghii also encourage the growth of beneficial fungi while limiting harmful ones, which enhances stress resistance and supports higher yields (Sun et al., 2023). 2.3 How rhizosphere microorganisms affect anoectochilus growth Rhizosphere microorganisms can dissolve essential nutrients such as nitrogen, phosphorus, and potassium from the soil, aiding Anoectochilus in their absorption. For example, AMF hyphae can extend beyond the root zone, allowing the roots to absorb more nutrients (Ning et al., 2020). Some bacteria, such as Pseudoatrobacitra and Actinomycetes, can also improve ammonia and potassium utilization, significantly aiding nutrient absorption in Anoectochilus roxburghii (Ning et al., 2020). Using fertilizers with a balanced nitrogen, phosphorus, and potassium ratio can increase the number of beneficial fungi, thereby improving plant growth and ginsenoside content (Sun et al., 2022). Some microorganisms can also secrete plant hormones, such as auxin, cytokinin and gibberellin. These hormones can stimulate root development and increase plant vitality. Hormones produced by microorganisms can also supplement the insufficient parts of plants, thus helping plants grow better (Wang et al., 2022). Some beneficial microorganisms can also regulate the hormone changes of plants in the face of drought or pest pressure, making plants more "resistant" (Ning et al., 2020). These microorganisms can also inhibit the bacteria in the soil and protect Anoectochilus roxburghii by competing or producing antibacterial substances. Bacillus subtilis can significantly reduce the number of Fusarium, thereby reducing the plant disease rate and improving the health level (Dong et al., 2018; Ning et al., 2020). Biochar application can also improve the rhizosphere environment, allow beneficial microorganisms to form a more complex ecological network, and inhibit the growth of harmful fungi (Liu et al., 2019a; 2019b).
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