Molecular Soil Biology 2025, Vol.16, No.1, 45-54 http://bioscipublisher.com/index.php/msb 47 3 Rhizosphere Microorganisms Promote the Growth of Anoectochilus Tissue Culture Seedlings 3.1 Rhizosphere microorganisms significantly enhance the growth of anoectochilus tissue culture seedlings After applying plant growth promoting rhizobacteria (PGPR) to Anoectochilus roxburghii tissue culture seedlings, the biomass of plants increased significantly, and some key nutrients in the soil became more abundant, which was conducive to the growth of roots and stems (Ji et al., 2018; fan et al., 2024). The root system of Anoectochilus roxburghii will secrete some substances, which will affect the species of microorganisms, making it easier for beneficial microorganisms to colonize around the root. This selective effect is helpful to increase the weight of roots and stems and the content of ginsenosides (Sun et al., 2023). In practice, biochar addition is a relatively effective method. It can alter the structure of rhizosphere microorganisms and improve soil quality. This not only increases root weight but also reduces the incidence of some root diseases, making the plant appear healthier and grow faster (Liu et al., 2022a; Liu et al., 2022b). 3.2 Which microorganisms are useful for A. roxburghii and their role in tissue culture Some microbes have shown clear benefits for A. roxburghii. For example, fungi from the Mortierella group are good at fighting off Fusarium oxysporum, a common plant disease. These fungi also help make phosphorus and other nutrients easier for the roots to take in, which is important for plant health (Wang et al., 2022). Another helpful microbe is Bacillus subtilis, a common PGPR. It can make the plant taller, help roots grow longer, and increase ginsenoside content (Ji et al., 2018). Arbuscular Mycorrhizal Fungi (AMF) are also worth mentioning. When AMF are used in biofertilizers, they help the plant take in more nutrients and change the microbe population around the roots. This helps increase the number of good microbes and reduce harmful ones in the soil (Ning et al., 2020). These microbes can be added into the tissue culture system if used properly. 3.3 How microorganisms affect important growth indicators of A. roxburghii Rhizosphere microorganisms can directly affect the root length, stem and leaf development and overall weight of Anoectochilus roxburghii. Bacteria such as PGPR can help the roots absorb nutrients faster by improving the availability of nutrients such as nitrogen and phosphorus in the soil, resulting in longer roots, thicker stems and stronger plants as a whole (Ji et al., 2018). These changes will also be reflected in the accumulation of ginsenosides, and the yield and quality will be improved. The use of biochar has also had a positive impact. It can make the species of rhizosphere microorganisms more abundant and stable, so as to enhance the absorption function and disease resistance of roots. This is beneficial to cultivate healthier and higher yield Anoectochilus roxburghii plantlets (Liu et al., 2022a; Liu et al., 2022b). 4 Mechanisms Promoting the Growth of Anoectochilus 4.1 Nitrogen fixation and microbial enhancement of nutrient utilization efficiency Rhizosphere microorganisms can transform nutrients in soil or air that plants cannot use into forms that Anoectochilus roxburghii can absorb. For example, some PGPR (plant growth promoting bacteria) can convert nitrogen in the air into nitrogen that Anoectochilus roxburghii can absorb, and release nutrients such as phosphorus and potassium, which are necessary for plant growth (PII et al., 2015; Hakim et al., 2021). Another mechanism is called "rhizosphere priming effect" (RPE), which stimulates the decomposition of organic matter in soil by secreting some organic matter from plant roots. These decomposition processes can accelerate microbial metabolism and increase the formation of microbial residues, thereby improving the supply efficiency of nitrogen in soil (Pausch et al., 2024). The interaction between root exudates and microorganisms is the key to maintain soil nutrient cycle, which is very beneficial to the root growth of Anoectochilus roxburghii. 4.2 Microbial hormone production promotes the growth of anoectochilus Beneficial bacteria in the rhizosphere can produce some hormones that promote plant growth, such as auxin and cytokinin. These hormones can make the roots of Anoectochilus roxburghii develop faster and have stronger absorption capacity, and promote the growth of stems and leaves (Ji et al., 2018; Hakim et al., 2021) (Figure 1).
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