Yizhi Sheng ^1* Xiangfeng Zeng ^2* Linduo Zhao ³ Yongbin Li ⁴

• ¹ China University of Geosciences, Beijing, China
• ² Institute of Applied Ecology, Chinese Academy of Sciences (CAS), Shenyang, Liaoning Province, China
• ³ Illinois Sustainable Technology Center. University of Illinois at Urbana-Champaign, Champaign, Illinois, United States
• ⁴ Dalian University of Technology, Dalian, Liaoning Province, China

conditions. These environments serve as critical transitional zones that support complex biogeochemical interactions between terrestrial and aquatic ecosystems. For instance, the complex interactions between organic matter and iron-bearing minerals at redox interfaces across diverse environments can either enhance or inhibit microbial and extracellular enzyme activity, thereby controlling the carbon budget in those transition zones (Dong et al., 2023;Sheng et al., 2022). In wetland transition zones between groundwater and lakes, processes such as dissimilatory nitrate reduction to ammonia are enriched, exhibiting seasonal variations in microbial activity (Chen et al., 2024). In the continental shelf sediments of China, denitrification is the primary pathway for dinitrogen gas production, followed by anaerobic ammonium oxidation (anammox) (Sun et al., 2021). In tropical oceans, biological nitrogen fixation is limited by iron-to-nitrogen ratios, with iron primarily sourced from land and mineral dust deposition (Wen et al., 2022). To counteract metal nutrient limitations, microorganisms have evolved strategies such as producing siderophores to acquire essential metals (e.g., Fe, Mo) from minerals for their growth (Sheng et al., 2023a;Zhou et al., 2024). Understanding how microbial communities and biogeochemical processes respond to both natural variations and human-induced disturbances in these environments is crucial.The ten published articles in this Research topic provide valuable insights into two main themes: (1) microbial community distribution responses to environmental variations, and (2) the impacts of anthropogenic activities on microbial processes, along with potential bioremediation and sustainable development strategies.The assembly of microbial communities demonstrates remarkable adaptability to fluctuating environmental conditions, including changes in temperature, pH, salinity, oxygen levels, nutrient availability, moisture, hydrodynamic disturbances, and contaminant stress (Sheng et al., 2016;Ruff et al., 2023;Chen et al., 2022;Shu and Huang, 2022). Liu et al. investigated bacterial community dynamics in oligosaline lakes, revealing that temporal succession was the primary driver of community assembly, with temperature, pH, and nitrate significantly influencing microbial structure and function across seasons. Shi et al. explored the effects of environmental gradients on microbial diversity and co-occurrence networks at various depths in Hulun lake, providing insights into nitrogen-cycling taxa and their habitat-specific adaptations in grassland lakes. Xian et al. highlighted the significant impact of water masses, identifiable body of water with a common formation history which has physical properties distinct from surrounding water, on the bacterial composition, topological characteristics and assembly process in the Yangtze River Estuary. This result may provide a theoretical foundation for predicting alterations in microbial communities within estuarine ecosystems under the influence of water masses. Brooks and Field studied responses of microbial communities in freshwater iron mats to hydrocarbon exposure and found that hydrocarbon pollution affects diversity, community structure, and resilience in contaminated ecotones. Guo et al. examined the effects of mining-induced soil fissures on microbial communities, showing that varying fissure conditions impacted soil moisture, pH, and nutrient availability, with rare species playing critical roles in maintaining microbial network stability.Nutrient and contaminant transformation through microbial degradation, redox reactions, and related processes can either intensify or mitigate their ecological effects. As mobile contaminants cross ecosystem boundaries, the role of microbial communities in detoxification and stabilization becomes crucial for sustaining ecological balance (Sheng et al., 2023b) Take together, this Special Issue advances our understanding of microbial metabolism, distribution, and the underlying drivers of microbial functions in both pristine and contaminated ecotones and similar environments. By integrating these findings, we will gain a better understanding of global nutrient cycles, contaminant bioremediation, and microbialenvironment interactions.