Genomics and Applied Biology 2024, Vol.15, No.5, 255-263 http://bioscipublisher.com/index.php/gab 258 4.2 Differential impact of each growth stage on major microbial groups Each growth stage of the rice plant differentially impacts major microbial groups in the rhizosphere. During the early stages of plant growth, certain species such as Herbaspirillum are more abundant in the rhizosphere compared to bulk soil. At the tillering stage, β-Proteobacteria, particularly aerobic, iron-oxidizing bacteria of the genus Sideroxydans, become predominant in the rhizosphere (Schmidt and Eickhorst, 2013). The flowering stage sees an increase in methanotrophic bacteria and methanogenic archaea, indicating a shift towards microbial groups involved in methane metabolism. Furthermore, the fungal community is notably enhanced in the rhizosphere compared to unplanted soil, with higher fungal-to-bacterial ratios observed throughout the growth stages (Hussain et al., 2018). These shifts suggest that different microbial groups are selectively enriched at various stages of plant development, influenced by root exudates and changing soil conditions (Asiloglu and Murase, 2016). 4.3 Ecological significance of dynamic changes in rhizosphere microbial community structure The dynamic changes in the rhizosphere microbial community structure have profound ecological significance. The enrichment of specific microbial groups at different growth stages can enhance nutrient cycling and soil health, thereby supporting plant growth and productivity. For example, the presence of iron reducers and fermenters in the rhizosphere can facilitate the breakdown of organic matter and improve nutrient availability. The seasonal shifts in microbial populations, such as the increase in methanotrophic bacteria during the flowering stage, play a crucial role in mitigating methane emissions from rice paddies, contributing to greenhouse gas regulation (Schmidt and Eickhorst, 2013). Additionally, the stable yet distinct microbial communities in the rhizosphere compared to bulk soil underscore the importance of the rhizosphere effect in shaping microbial diversity and function. Overall, understanding these dynamic changes can inform strategies to optimize microbial interactions for sustainable rice cultivation and environmental management (Fu et al., 2023; Ding et al., 2019). 5 Environmental Factors Influencing Rhizosphere Microbial Communities 5.1 Variability in major environmental parameters, such as soil temperature, moisture, and pH The structure and function of microbial communities in the rice rhizosphere are significantly influenced by various environmental parameters, including soil temperature, moisture, and pH. Soil pH, in particular, has been identified as a critical factor affecting the diversity and composition of rhizosphere bacterial communities. Studies have shown that soil pH can explain a substantial portion of the variation in microbial community structure, with different pH levels fostering distinct microbial populations (Deng et al., 2017; Han, 2024). For instance, acidic soils (pH<5.5) tend to support different bacterial communities compared to neutral or alkaline soils, affecting both the diversity and functional capabilities of these communities (Wan et al., 2020). Additionally, soil moisture and temperature also play crucial roles, although their specific impacts on microbial community dynamics in the rice rhizosphere are less well-documented compared to pH (Lopes et al., 2021). 5.2 Regulatory effects of different environmental factors on rhizosphere microbial composition Environmental factors such as soil type, nutrient levels, and climatic conditions have regulatory effects on the composition of rhizosphere microbial communities. Soil type has been shown to be a primary determinant of bacterial community structure, with different soil types (e.g., Albic, Black, and Chernozem) hosting distinct microbial populations (Zhang et al., 2021). Soil nutrients, particularly nitrogen forms (NH4-N, NO3-N, NO2-N, and TN), also significantly influence microbial community composition, especially for bacteria and archaea (Deng et al., 2017). Climatic factors, including temperature and precipitation, further modulate these effects by altering soil properties and nutrient availability, thereby shaping the microbial community structure in the rhizosphere (Figure 2) (Zhang et al., 2021). 5.3 Influence of seasonal environmental changes on microbial metabolic activity and community stability Seasonal changes in environmental conditions, such as temperature and moisture, can lead to shifts in microbial metabolic activity and community stability in the rice rhizosphere. The microbial community in the rhizosphere is generally more dynamic and responsive to these changes compared to bulk soil. For example, the abundance of certain microbial taxa, such as potential iron reducers and fermenters, can fluctuate with plant growth stages and associated environmental changes. Moreover, the stability of microbial communities is influenced by the
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