Comparing litter dynamics of Phragmites australis and Spartina alterniflora in a sub-tropical Chinese estuary: Contrasts in early and late decomposition

• Spartina alterniflora litter decomposes faster than Phragmites australis.
• Decomposition starts whilst these macrophytes remain standing.
• Decomposition speeds up on transfer to the sediment surface.
• Decomposition rates are also affected by litter quality.

Litter decomposition in communities dominated by emergent macrophytes can be considered a two-phased decomposition process, a standing phase followed by decay on the sediment surface. We examined the decomposition and nutrient dynamics in both phases of three structural components (leaves, flowers, stems) of two common emergent macrophytes in the Min River estuary, southeast China. The two species were Phragmites australis, a native species, and Spartina alterniflora an invasive one. Decomposition was slower in the standing phase compared to the sediment surface phase for most structural components of both species. In the standing and sediment surface phase, the exponential breakdown rates (k-value) for all structural components of S. alterniflora were much greater than the corresponding values for P australis. The k-values in different components of P. australis and S. alterniflora ranged from 0.96 to 1.79 × 10−3 d−1 and 1.67 to 4.58 × 10−3 d−1 in the standing phase, and from 1.60 to 5.32 × 10−3 d−1 and 3.05 to 6.93 × 10−3 d−1 in the sediment surface phase, for the two species, respectively. Over the 210 day study, the litter carbon concentrations in three structural components of P. australis fluctuated considerably compared to S. alterniflora. The variations in nitrogen concentration of flower and stem litter in both species experienced a similar pattern throughout the experimental period, in the sediment surface phase, although the nitrogen concentration increased in both species. Litter phosphorus concentration showed a completely different pattern between the two species throughout.