Nitrogen-Enriched Eutrophication Promotes the Invasion of Spartina alterniflora in Coastal China

Abstract

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. It could be shown that the long term per m2 biomass of Spartina alternifolia changes are significantly correlated with human-induced increases of the inorganic nitrogen level in the Chinese coastal water. These results support the hypothesis that through enhanced photosynthesis, leaf area index, sexual and asexual growth as well as enhanced biomass accumulation and inter-specific competitive ability, in formerly vegetated upland marshes, non-vegetated mud flats, and the salt marsh areas, nitrogen eutrophication of coastal waters potentially promotes the spread of Spartina in China.