Genomics and Applied Biology 2024, Vol.15, No.5, 255-263 http://bioscipublisher.com/index.php/gab 256 2 Composition and Function of the Rice Rhizosphere Microbial Community 2.1 Key microbial groups and their ecological roles The rice rhizosphere hosts a diverse array of microbial groups, including bacteria, fungi, and actinomycetes, each playing crucial ecological roles. Bacterial communities are particularly abundant and diverse, with key phyla such as Proteobacteria, Acidobacteria, Actinobacteria, andBacteroidetes being predominant (Breidenbach et al., 2016). These bacteria are involved in various processes, including nutrient cycling and organic matter decomposition. Fungi, including Ascomycota and Basidiomycota, also play significant roles in the rhizosphere, contributing to nutrient cycling and plant health (Wei et al., 2023). Actinomycetes, known for their ability to decompose complex organic materials, are another important group in the rhizosphere (Oliveira et al., 2022). 2.2 The role of microbial communities in nutrient cycling Microbial communities in the rice rhizosphere are integral to nutrient cycling, particularly for nitrogen (N) and phosphorus (P). Bacteria such as those from the genera Geobacter and Anaeromyxobacter are involved in iron reduction, which is closely linked to nutrient availability (Breidenbach et al., 2016). Nitrogen cycling is facilitated by various microbial processes, including nitrogen fixation, nitrification, and denitrification. For instance, certain bacteria in the rhizosphere possess genes related to denitrification, enhancing nitrogen availability for rice plants (Pramanik et al., 2020). Phosphorus cycling is also mediated by microbial activity, with some microbes capable of solubilizing phosphate, making it more accessible to plants. The interactions between these microbial processes and the redox conditions in the rhizosphere further influence nutrient dynamics (Wei et al., 2019). 2.3 The potential role of microbes in rice rhizosphere health and disease resistance Microbial communities in the rice rhizosphere contribute significantly to plant health and disease resistance. Beneficial microbes can suppress soil-borne pathogens through competitive exclusion, production of antimicrobial compounds, and induction of plant defense mechanisms (Ding et al., 2019). For example, certain strains of Herbaspirillum are consistently more abundant in the rhizosphere and are known to promote plant growth and health (Breidenbach et al., 2016). Additionally, the microbial diversity and network complexity in the rhizosphere can enhance resilience against environmental stresses and pathogen invasion. The presence of specific microbial groups, such as sulfate-reducing and sulfur-oxidizing bacteria, also plays a role in mitigating arsenic toxicity, thereby protecting rice plants from harmful effects (Zecchin et al., 2023). 3 Seasonal Stages and Microbial Community Changes 3.1 Criteria for dividing the growing season The growing season of rice can be divided into several distinct stages: seedling, tillering, heading, and maturation. These stages are critical for understanding the dynamics of microbial communities in the rhizosphere. The seedling stage marks the initial growth phase, followed by the tillering stage where the plant begins to produce multiple stems. The heading stage is characterized by the emergence of the rice panicles, and finally, the maturation stage is when the grains fully develop and ripen (Schmidt and Eickhorst, 2013; Breidenbach et al., 2016; Wang et al., 2019). 3.2 Key environmental factors affecting microbial communities at each stage Several environmental factors influence the microbial communities in the rice rhizosphere at different growth stages. Soil pH, nitrogen availability, and soil texture are significant factors that shape the microbial community structure. For instance, soil pH has been shown to be a major determinant of bacterial and archaeal community composition, while nitrogen levels influence microbial population dynamics and functional capabilities (Deng et al., 2017; Wang et al., 2019). Additionally, root exudates, which vary with plant growth stages, play a crucial role in shaping the microbial community by providing specific nutrients and signaling molecules (Li et al., 2019; Berg and Smalla, 2009). During the seedling stage, the microbial community is influenced by initial soil conditions and the early root exudates, which are rich in simple sugars and organic acids. As the plant progresses to the tillering stage, the microbial community becomes more diverse, with an increase in aerobic bacteria such as β-Proteobacteria, which
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