关键词: 辽河口湿地, 植被类型, 高通量测序, 土壤微生物, 微生物多样性, 群落结构

Abstract:

Rhizosphere microbial communities play a crucial role in wetland ecosystems by interacting with plant roots and influencing various aspects of plant growth, including nutrient uptake, resistance to environmental stressors, and the overall ecosystem function. These communities are complex and dynamic, driven by interactions between microorganisms and plants, and further influenced by soil physicochemical properties and environmental conditions. The rhizosphere is a hotspot for microbial activity, where microbes help plants acquire nutrients, degrade organic matter, and provide resistance to pathogens. Understanding the diversity, structure, and functional roles of these microbial communities across different wetland types is essential to understand the ecological processes that support wetland biodiversity, ecosystem stability, and resilience. Wetlands are valuable ecosystems that provide essential services such as carbon sequestration, water filtration, and habitat for biodiversity. In coastal wetlands where plants such as Phragmites australis and Suaeda salsa are commonly found, rhizosphere microbial communities are integral to the health of these ecosystems. Investigating the diversity and structure of these microbial communities across various wetland types, along with identifying the key factors that influence them, is crucial for understanding how these ecosystems function and are conserved in the face of ongoing environmental changes. The Liaohe Estuary Wetland, located in northern China, was selected as the research area for this study. This wetland encompasses a range of vegetation zones with distinct ecological characteristics. Soil samples were collected from five different wetland types: the Phragmites australis distribution zone (P. australis rhizosphere soil, D1), the interlaced P. australis and S. salsa zone (P. australis rhizosphere soil, D2), the interlaced P. australis and S. salsa zone (S. salsa rhizosphere soil, D3), the S. salsa distribution zone (S. salsa rhizosphere soil, D4), and tidal flat sediments (D5). These zones were selected based on their distinct vegetation types and potential to represent a variety of wetland conditions. To assess the microbial diversity and community structure in these soils, Illumina MiSeq PE300 high-throughput sequencing technology was employed based on 16S rRNA gene sequencing. This method is widely used in microbial ecology to obtain a comprehensive understanding of microbial community composition as it provides detailed taxonomic information at the species level. The sequencing data allowed for a detailed analysis of the microbial communities in the rhizosphere soils and a subsequent comparison of these communities across different wetland types. The results of this study revealed that different vegetation types significantly affected the physicochemical properties of the soil as well as the structure and function of the rhizosphere microbial communities. Soil samples from D1, which were dominated by P. australis, had a significantly higher organic matter content than the other samples. Conversely, soil from D5, which consisted of tidal flat sediments, exhibited a significantly higher total nitrogen content. These differences in soil properties are likely to influence the microbial community composition and functional potential, as different microbial groups may be adapted to thrive under specific environmental conditions. A total of 40 phyla, 95 classes, 184 orders, 311 families, 528 genera, and 888 species of soil microbes were identified across the rhizosphere soils of the five vegetation types in the Liaohe Estuary Wetland. These findings highlight the vast microbial diversity present in wetland rhizospheres. Among the identified phyla, Proteobacteria, Bacteroidetes, Actinobacteria, and Chloroflexi were dominant in all soil samples. Notably, Proteobacteria exhibited a significantly higher abundance than other phyla, making it the most dominant phylum in all samples. This is consistent with previous studies in other wetland ecosystems, where Proteobacteria have often been identified as a dominant group owing to their broad metabolic capabilities and adaptability to various environmental conditions. At the class level, microbial communities displayed greater specificity. For example, β-Proteobacteria were the dominant class in D1, whereas γ-Proteobacteria were dominant in the other four samples. This variation in microbial community composition at the class level suggests that environmental factors, such as soil moisture content, nutrient availability, and plant root exudates, can shape the microbial community structure in the rhizosphere. The relative abundances of the dominant and sub-dominant classes were relatively consistent across the samples, indicating a balanced microbial community without a clear absolute dominant class. This observation highlights the complexity of microbial interactions in the rhizosphere, where multiple groups may coexist and contribute to ecosystem function. No significant correlation was found between soil environmental factors and microbial diversity or richness across different wetland types. However, nitrite nitrogen content exhibited a stronger correlation with microbial diversity, whereas organic matter content was more strongly correlated with microbial richness. These results showed that microbial diversity and richness are influenced by a combination of factors; some environmental variables, such as nitrogen availability and organic matter, may play more significant roles in shaping the microbial community structure. This is consistent with the known role of nitrogen as a key nutrient for microbial growth and metabolism in soil environments. Redundancy analysis revealed that total nitrogen, organic matter, and chloride ion content were the primary factors influencing the microbial community structure in rhizosphere soils. These factors are crucial for the growth and development of microorganisms because they provide essential nutrients and affect the physical and chemical properties of the soil, which in turn affect microbial activity. Further analysis of soil environmental factors and their impact on the distribution of dominant microbial phyla indicated that microbial communities respond differently to environmental conditions. For example, increases in soil water content, oxidation-reduction potential, organic matter, and nitrite-nitrogen content enhance the availability of nutrients and moisture, which are necessary for microbial growth and development. These factors were found to significantly affect the microbial community structure, leading to changes in microbial composition and functional diversity. This underscores the importance of environmental factors in shaping the microbial communities in coastal wetland ecosystems. The findings of this study provide valuable insights into the ecological functions of the rhizosphere microbial communities in wetland ecosystems. The results demonstrate that vegetation type and soil physicochemical properties play critical roles in shaping microbial community structure and function. By understanding the factors influencing microbial communities, we can better understand the ecological processes that sustain wetland biodiversity and ecosystem stability. This knowledge is crucial for the conservation and management of coastal wetlands in northern China as it provides a theoretical foundation for maintaining ecological integrity and resilience in the face of environmental changes.

Key words: Liaohe Estuary Wetland, vegetation types, high-throughput sequencing, soil microbial, microbial diversity, community structure