Salinity exerted little effect on decomposition of emergent macrophytes in coastal peatlands

Climate-warming-driven sea level rise may change the vegetation composition of coastal wetlands, influencing ecosystem functions including photosynthetic activity, biomass production, litter decomposability and nutrient cycling. Litter decomposition rates of the most dominant macrophytes, Phragmites australis, Carex sp. and Schoenoplectus tabernaemontani, in two nearby freshwater and oligohaline peatlands were compared to determine the impact of salinity on litter decomposition. Electrical conductivity difference of 1.2-8.0 mS cm(-1) (mean difference = 4.8 mS cm(-1)) between freshwater and oligohaline peatlands did not significantly affect the decomposition of macmphyte litter. Between species, S. tabernaemontani lost a significantly higher mass (29%) in the first month of decomposition compared to P. australis and Carex sp. Overall, litter decay rates for S. tabernaemontani was k = 0.0064-0.0078 d(-1) while P. australis and Carex sp. both had k = 0.0017-0.0028 d(-1). After one year, S. tabernaemontani litter was totally decomposed while the other species had 40-60% mass remaining relative to their initial dry mass confirming that P. australis and Carex sp. contribute to peat formation while S. tabernaemontani does not. Apparent differences in decomposition kinetics between S. tabernaemontani and the other species tested indicated that litter quality, especially C:P, C:N, N:P and C:Ca, is of great importance for both microbial colonization (initial phase) as well as for sustaining decomposition after colonization. This study shows that litter quality controls litter decomposition more than narrow salinity ranges. Hence, we suggest that sea level rise, combined with increased precipitation, may not have significant impact on the decomposition of these macmphytes in the future. However, sea level rise may lead to changes in vegetation composition replacing the peat-forming species by S. tabernaemontani which favors relatively deep, oligohaline wetlands. This would eventually affect carbon sequestration rates.

Automated summary

The study found that salinity did not significantly affect litter decomposition rates, while litter quality had a significant impact. Schoenoplectus tabernaemontani lost the most mass during decomposition and was completely decomposed after one year, contrasting with Phragmites australis and Carex sp. which retained 40-60% of their initial mass after one year.