Molecular Soil Biology 2024, Vol.15, No.2, 87-98 http://bioscipublisher.com/index.php/msb 88 2 Soil Microbiota in Rice Cultivation Soil microbiota are integral to the sustainability and productivity of rice cultivation systems. These microorganisms, which include bacteria, fungi, archaea, and other microorganisms, are responsible for a range of ecological functions that support the growth and health of rice plants. The intricate relationships between these microorganisms and the rice plants they interact with are vital for nutrient cycling, plant growth promotion, and the maintenance of soil structure and fertility. Understanding the diversity and function of these microorganisms is essential for improving rice yield and sustainability, particularly in the context of global food security challenges. The unique flooded conditions of rice paddies create a specialized environment where these microorganisms thrive, contributing to both the positive and negative outcomes in rice agriculture. The study of soil microbiota in rice systems not only enhances our understanding of these ecosystems but also provides insights into how we can manipulate these microorganisms to achieve better agricultural outcomes, reduce greenhouse gas emissions, and promote long-term soil health. 2.1 Types of soil microorganisms relevant to rice (e.g., bacteria, fungi, archaea) Rice paddies are home to a diverse range of soil microorganisms, each playing distinct roles within the ecosystem. Bacteria, including nitrogen-fixing species like Rhizobium and Azospirillum, are crucial for converting atmospheric nitrogen into ammonia, which rice plants can then utilize for growth. Phosphate-solubilizing bacteria such as Pseudomonas are also essential, transforming insoluble forms of phosphorus into bioavailable forms. These bacterial communities are complemented by fungi, particularly mycorrhizal fungi, which form symbiotic relationships with rice roots. These fungi enhance nutrient uptake, particularly phosphorus, and provide protection against soil-borne pathogens. Archaea, especially methanogenic archaea, are key players in the carbon cycle within flooded rice paddies, where they contribute to methane production—a significant greenhouse gas. The unique conditions of flooded paddies foster a distinct microbial community that is highly adapted to anaerobic conditions, allowing these microorganisms to thrive and perform essential ecological functions. This microbial diversity is not just critical for nutrient cycling but also for maintaining the balance of the ecosystem, influencing everything from soil structure to plant health (Edwards et al., 2015; Ding et al., 2019). 2.2 Roles and functions of soil microbiota in the rice ecosystem 2.2.1 Nutrient cycling (nitrogen fixation, phosphorus solubilization) Soil microbiota in rice paddies are indispensable for maintaining the health and productivity of the rice ecosystem. These microorganisms are involved in several critical functions that contribute to the overall sustainability of rice cultivation. One of the primary roles of soil microbiota in rice ecosystems is nutrient cycling, particularly through processes such as nitrogen fixation and phosphorus solubilization. Nitrogen-fixing bacteria, such as those in the genera Rhizobium and Azospirillum, play a crucial role by converting atmospheric nitrogen into ammonia, which is then used by rice plants to support growth and development. This process is vital for sustaining the nitrogen balance in paddy soils, where synthetic nitrogen fertilizers are often expensive or environmentally damaging. Similarly, phosphate-solubilizing bacteria like Pseudomonas convert insoluble phosphorus compounds into soluble forms that rice plants can absorb, thereby supporting robust plant growth. These nutrient cycling processes are essential not only for plant health but also for maintaining soil fertility over time, as they reduce the need for chemical fertilizers and enhance the natural fertility of the soil (Rao, 2018; Jiao et al., 2019). 2.2.2 Plant growth promotion (phytohormone production, disease resistance) In addition to their role in nutrient cycling, soil microbiota are also crucial for promoting plant growth and enhancing disease resistance in rice plants. Certain rhizosphere bacteria produce phytohormones, such as auxins, gibberellins, and cytokinins, which stimulate root development and improve the plant’s ability to absorb nutrients. These phytohormones are key to optimizing root architecture, thereby enhancing the plant’s access to water and nutrients. Furthermore, soil microbiota can induce systemic resistance in rice plants, making them more resilient to a variety of pathogens.
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