Functional gene dynamics and methane cycling across vegetation types in coastal soils of Gujarat, India

Wetland soils play a crucial role in global methane (CH₄) cycling, yet the influence of soil depth and different vegetation types on microbial functional gene abundance, enzyme activities, and potential CH₄ production remains poorly understood in the inter-tidal coastal areas. The present study investigated potential CH₄ production across different vegetation types (barren, halophyte, and mangrove) at two coastal sites in Gujarat (Diu and Sartanpar), India. This study further highlights the relationships between soil characteristics, enzyme activities (β-glucosidase, alkaline phosphatase, and sulfatase), and functional gene abundance (pmoA, mcrA, and dsrA) to understand their role in CH₄ dynamics. Our findings revealed that the CH₄ production was significantly higher in Diu as compared to Sartanpar (2862 and 1125.1 µg C kg^-1 soil day^-1 respectively). Mangrove soils showed the highest enzymatic activities and CH₄ production among all vegetation at 60-80 cm of depth (2544.54 µg C kg^-1 soil day^-1). The pmoA gene abundance slightly declined with depth, whereas the mcrA gene remained constant throughout the soil profile at both sites. The mcrA gene showed a positive and significant correlation with soil moisture (r = 0.82), OC (r = 0.57), NH₄⁺ (r = 0.83), K⁺ (r = 0.32), P (r = 0.21), Na⁺ (r = 0.36), and SO₄^2- (r = 0.34) while negatively with pH (r = - 0.50) and NO₃^- (r = - 0.52). Higher pmoA/mcrA and dsrA/mcrA ratios were linked with lower CH₄ production, suggesting a regulatory role of CH₄ oxidation and sulfate reduction during CH₄ production. Overall, our study highlights the interplay between soil properties, microbial functional genes, and enzyme activities in regulating CH₄ across different vegetation types and soil depths in Indian intertidal coastal soils, an ecosystem which is underrepresented. This study provides new insights into how vegetation-driven microenvironments and depth-dependent microbial processes together shape CH₄ cycling in coastal wetlands.