38 Chapter 1 KNOWLEDGE GAPS ON METHANOTROPHIC RESPONSE TO COASTAL-STRESSORS Despite significant progress in understanding methane cycling in coastal ecosystems, several key knowledge gaps remain. First, while the roles of aerobic and anaerobic methanotrophs are well-established, the physiological limits of these microorganisms under stress conditions such as sulfide toxicity and salinity stress are poorly understood. For example, the mechanisms by which sulfide inhibits methanotrophic activity and the potential for microbial adaptation to sulfidic environments remain largely unexplored and are therefore addressed in Chapters 2, 4, and 5. In this regard, the putative coupling of S-AOM with “Ca. Methanoperedens” in the sulfate-containing sediments of Lake Cadagno is relevant and, this coupling was further explored in Chapter 7. Additionally, the impact of sea-level rise on methane biofilter efficiency, particularly in coastal systems, warrants further investigation and is addressed in Chapter 3 and 6. Although some freshwater methanotrophs have been shown to withstand marine salinities, the overall resilience of these communities in the face of increasing salinity gradients is not fully understood. Finally, there is a need for more detailed studies on the interplay between eutrophication, sulfide accumulation, salinity increase and methane oxidation rates. While elevated organic matter inputs clearly enhances methanogenesis, the long-term effect on methane biofilter functioning, particularly in relation to microbial community shifts and enzyme inhibition and overall physiological adaptations are not yet well explored These knowledge gaps are critical for developing accurate and predictive models of methane emissions and for designing effective management strategies to mitigate greenhouse gas emissions from vulnerable coastal ecosystems.
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