Pollution‐driven eutrophication is a significant by‐product of rapid economic growth in China. Such environmental changes have huge consequences on local biodiversity and ecosystem functions through the spread of invasive introduced species. Spartina alterniflora has been spreading quickly and extensively throughout China since the mid 1980s, soon after its intentional introduction from the eastern United States. The range expansion of S. alterniflora coincides with a significant increase in the per unit standing biomass of the species in the Chinese coastal wetlands from the 1980s to 2000s. Here we showed that the long term per m2 biomass of S. alternifolia changes are significantly correlated with human‐induced increases of the inorganic nitrogen level in the Chinese coastal water. We established this causal relationship by showing that reproduction, growth, and biomass of individual S. alterniflora, grown in experimental tanks, increased with higher levels of soil inorganic nitrogen. Competition experiments indicated that S. alterniflora out competed Phragmites australis at both low and high soil nitrogen levels. These field and experimental based results support the hypothesis that nitrogen‐enriched eutrophication contributed significantly to the successful invasion of S. alterniflora in China.
Terrestrial ecosystems carbon (C) and nitrogen (N) cycles, affected by plant invasion, are not fully understood. In this study, the impact of 10 years Spartina alterniflora invasion on soil organic matter (SOM), labile, and recalcitrant pools was examined comparing with bare flat and native Suaeda salsa and Phragmites australis communities in tidal salt marshes of the Eastern Chinese coast. Short‐term S. alterniflora invasion significantly raised C and N concentrations in SOM, labile and recalcitrant pools compared to bare flat, S. salsa and P. australis soils. Spartina alterniflora soil had higher recalcitrant index for C relative to bare flat. The proportion of S. alterniflora‐derived C and the decomposition rate of old C in the labile pool were significantly higher than those in the recalcitrant pool. However, the S. alterniflora‐derived C stock of the recalcitrant pool was much greater than that of the labile pool. The SOM and recalcitrant pools in S. alterniflora soil had significantly higher δ15N levels compared with bare flat, indicating an increased N loss following S. alterniflora invasion. The results suggested that short‐term S. alterniflora invasion significantly enlarged soil organic C and N pools via altering SOM input and decomposition.
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