Dynamics of litter decomposition of dieback Phragmites in Spartina-invaded salt marshes

Vegetation dieback can alter plant population dynamics and community structure, however, its impact on litter decomposition has been poorly understood. The litterbag method was employed to examine effects of reed dieback on litter decomposition of native Phragmites australis in the Spartina alterniflora-invaded Chinese salt marshes. Compared with healthy Phragmites, the initial C and N contents in leaf, sheath and stem of dieback Phragmites were significantly higher (for all P < 0.001, except N content in stem P > 0.05) and their initial C:N ratios were significantly lower (P < 0.05). Moreover, the aerial stem litter of dieback Phragmites decomposed significantly faster than that of healthy Phragmites (F1,46 = 5.784; P < 0.05). During the 310-day decomposition, the C:N ratio in dieback Phragmites was significantly lower than that in healthy Phragmites (F1,273 = 28.510, P < 0.001) and the remaining N concentrations of the two types of Phragmites were significantly different from each other (F1,270 = 16.316, P < 0.001). Only the N content in leaf tissue of dieback Phragmites decreased continuously, while it changed up and down in other tissues. Our results suggest the significance of integrating vegetation dieback into the ecosystem processes and the vegetation and land-surface models, as well as the management strategies on protecting the susceptible ecosystems.