Variable decomposition of two plant litters and their effects on the carbon sequestration ability of wetland soil in the Yangtze River estuary

Highly efficient sequestration of carbon into soil by plants is crucial to wetland ecosystems under rising atmospheric CO2. The carbon sequestration ability of wetland can be roughly evaluated from the amount of carbon fixed through planes photosynthesis, but the decomposition properties of plant litter returning to soil are also essential to its evaluation. We examined litter decomposition of Phragmites australis (P. australis) and Spartina alterniflora (S. alterniflora), two dominant plants from Jiuduansha wetland in the Yangtze River estuary, returned to soil in-situ and ex-situ, to clarify their effect on soil respiration and carbon sequestration efficiency. Both mass and carbon content of S. alterniflora were lost faster than P. australis when their plant litters were returned to soil. Soil type exerted a significant effect on litter decomposition but not on plant ranking for decomposition rate (k). High moisture and low nitrogen content in the wetland soils resulted in the lower decomposition rates of litter, compared with inland soils. Litter properties were determining factors in ranking of decomposition rate, in which the k was negatively correlated with the lignin/N and C/N ratios, and positively correlated with the initial nitrogen content. P. australis had low nitrogen content, high lignin/N and C/N ratios, so it had the lower decomposition rate and soil respiration. Combine the plant biomass, litter decomposition and soil respiration, P. australis wetland possesses the higher carbon sequestration ability in the Yangtze River estuary than S. alterniflora wetland.