Nitrogen Uptake and Use Efficiency of Invasive Spartina alterniflora and Native Phragmites australis: Effect of Nitrogen Supply

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AbstractPlant roots play a vital role in acquisition of resources, while their potential role in plant successful invasions has been largely overlooked. Spartina alterniflora is an invasive grass that has expanded dramatically on the Chinese coast, outcompeting native plant Phragmites australis and resulting in serious negative consequences for invaded ecosystems. In this study, we evaluated differences between S. alterniflora and P. australis in nitrogen uptake and use efficiency as well as plasticity of nitrogen characteristics and additional morphological traits in response to increased nitrogen supply. We grew two species in monoculture and mixed‐culture pots under two nitrogen levels in a greenhouse environment. After growing for 17 weeks, plants were exposed to 15N‐labeled ammonium chloride for 48 h and harvested to compare the uptake of nitrogen. Invasive S. alterniflora showed significantly higher biomass, root mass ratio, and nitrogen use efficiency but lower 15N uptake rate than native P. australis in both monocultures and mixed‐cultures, regardless of nitrogen levels. Nitrogen supply significantly increased biomass, total 15N uptake, and 15N uptake rate but decreased root mass ratio and nitrogen use efficiency of both species regardless of culture form, with biomass and total 15N uptake of S. alterniflora responding more strongly to nitrogen supply than the corresponding traits of P. australis when the two species were grown in a mixed culture. Our results suggested that the greater root mass ratio and nitrogen use efficiency of S. alterniflora played a greater role than root nitrogen capture capacity in its successful invasion.