Effects of litter decomposition on sedimentary organic carbon sequestration in invasive and native halophyte marshes of Ganghwa, Korea

Litter decomposition is a critical driver of carbon cycling in tidal flats, yet the extent to which decomposed organic carbon is sequestered in sediments remains unclear. We studied the effects of invasive Spartina alterniflora and native Phragmites australis litter decomposition on sedimentary organic carbon sequestration. Litterbag experiments were conducted over 360 days in tidal flats. Decomposition patterns were classified as rapid, moderate, and slow. Over 60 % of the litter carbon decomposed within the first 60 days in salt marsh (vegetated). In the bare tidal flat (unvegetated), S. alterniflora litter decomposed faster than P. australis litter. Bacterial composition shifted over time, being dominated sequentially by Bacteroidales, Bacillales, and then Pseudomonadales. Habitats with low Bacteroidales abundances showed lower initial decomposition rates. The decomposed carbon showed limited mobility and remained near the litter. These findings provide insights into the effects of litter decomposition on sedimentary organic carbon and its dynamics within sediments.