Molecular Microbiology Research 2024, Vol.14, No.5, 248-258 http://microbescipublisher.com/index.php/mmr 249 2 Overview of the Rhizosphere The rhizosphere is a complex and dynamic environment where plant roots interact with a diverse array of microorganisms. These interactions are influenced by a multitude of factors, including soil properties, plant genotype, and environmental conditions, all of which collectively shape the microbial community composition and functionality in the rhizosphere. 2.1 Definition and characteristics of the rhizosphere The rhizosphere is the narrow region of soil that is directly influenced by root secretions and associated soil microorganisms. It is a dynamic environment where complex interactions between plant roots, soil, and microorganisms occur, significantly impacting plant health and growth. The rhizosphere is often referred to as the plant's second genome due to the extensive microbial diversity it harbors, which can include tens of thousands of microbial species (Berendsen et al., 2012; Mendes et al., 2013). This zone is crucial for nutrient cycling, disease suppression, and overall plant vitality (Philippot et al., 2013). 2.2 Composition of rhizosphere microbial communities The microbial communities in the rhizosphere are highly diverse and include bacteria, fungi, archaea, and other microorganisms. These communities are not randomly assembled but are selectively influenced by the plant species and even specific cultivars (Berendsen et al., 2012; Rotoni et al., 2022). For instance, in kiwifruit, long-term organic fertilization has been shown to increase bacterial diversity and the relative abundance of plant growth-promoting bacteria such as Pseudomonas and Burkholderia, while reducing the abundance of plant pathogenic fungi like Fusarium(Liu et al., 2020). Similarly, the rhizosphere of Artemisia annua is enriched with plant growth-promoting bacteria such as Sphingomonas and Sphingobium, which are critical for the plant's adaptation to its environment (Shi et al., 2021). 2.3 Factors influencing rhizosphere microbial diversity Several factors influence the diversity and composition of rhizosphere microbial communities. These include soil pH, nutrient availability, soil texture, and environmental conditions. For example, soil pH and nitrogen levels are significant determinants of bacterial and archaeal community structures, while soil texture and heavy metals can also play crucial roles (Deng et al., 2017). Plant genotype is another critical factor; different cultivars can select for distinct microbial communities, as seen in studies with chrysanthemum cultivars (Rotoni et al., 2022). Additionally, organic amendments and sulfur applications have been shown to alter microbial community structures, enhancing beneficial microbial taxa and reducing disease incidence in kiwifruit (Liu et al., 2020; Yang et al., 2022). 3 Microbial Interactions in the Rhizosphere The rhizosphere is a dynamic environment where microbial interactions play a crucial role in plant health and productivity. Understanding these interactions can lead to the development of sustainable agricultural practices that enhance crop yield and resilience. 3.1 Symbiotic relationships 3.1.1 Mycorrhizal associations Mycorrhizal fungi form mutualistic associations with plant roots, enhancing nutrient uptake, particularly phosphorus, and improving plant stress tolerance. These fungi extend the root system through their hyphal networks, facilitating greater access to soil nutrients and water. Mycorrhizal associations are crucial for sustainable agriculture, especially under stressful environmental conditions, as they help maintain plant growth and soil health (Nadeem et al., 2014). 3.1.2 Nitrogen-fixing bacteria Nitrogen-fixing bacteria, such as those in the genera Rhizobiumand Azospirillum, convert atmospheric nitrogen into a form that plants can use. This symbiotic relationship is vital for plant growth, especially in
RkJQdWJsaXNoZXIy MjQ4ODYzNA==