Regional Disparities and Vegetation Impact on Microbial Communities in Constructed Wetlands: A Methane Cycle Perspective

Constructed wetlands provide critical ecosystem services, including nutrient retention and greenhouse gas (GHG) regulation. However, the influence of regional differences and winter vegetation cover on microbial community dynamics and methane (CH4) cycling remains poorly understood. This study examines CH4 emissions and microbial community composition in 34 agricultural-constructed wetlands across two Swedish regions (Halland and Malardalen) during winter. Surface water chemistry, CH4 concentrations, and microbial community structure were analyzed, with a focus on vegetated versus unvegetated areas. Microbial communities exhibited distinct regional patterns, with Malardalen wetlands showing lower bacterial diversity but higher CH4 concentrations compared to Halland. Vegetation influenced microbial diversity, particularly in Halland, where vegetated areas supported greater bacterial richness, including methanotroph-associated taxa. However, correlations between CH4, methanotroph abundance, and environmental variables varied by region, indicating site-specific controls on CH4 cycling. These findings highlight the need for regionally tailored wetland management strategies to optimize CH4 mitigation, particularly in cold climates where winter conditions significantly shape microbial processes.