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

Abstract

Research ArticleNitrogen Uptake and Use Efficiency of Invasive Spartina alterniflora and Native Phragmites australis: Effect of Nitrogen Supply Plant 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 15 N-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 15 N uptake rate than native P. australis in both monocultures and mixed-cultures, regardless of nitrogen levels. Nitrogen supply significantly increased biomass, total 15 N uptake, and 15 N uptake rate but decreased root mass ratio and nitrogen use efficiency of both species regardless of culture form, with biomass and total 15 N 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. IntroductionWith increasing globalization, the damaging influences of invasive species on native ecosystems and biota have become a prevalent concern [1-3], and understanding the mechanisms of species invasion has become a priority in order to control and prevent their spread. To identify traits associated with invasiveness, many studies comparing invasive and native plant species have been conducted emphasizing morphology [4][5][6][7], photosynthesis [4, 7-9], breeding systems [6, 10], flowering phenology [9], propagule size [6,7,11], and phenotypic plasticity [4,12,13]. However, the potential role of roots in the success of plant invasions has been largely overlooked. Plant roots play a vital role in the uptake of nutrients and other resources, and root plasticity is one of the central mechanisms for plant resource exploitation and acquisition [14].Resource capture capacity of roots varies substantially among species [15][16][17], yet few studies have compared the differences in resource uptake and physiological plasticity of roots responding to different resource levels between invasive and native plants [16,18]. In China, the invasive C 4 grass species smooth cordgrass (Spartina alterniflora) is receiving increasing attention. The spe...

Invasive knotweed has greater nitrogen-use efficiency than native plants: evidence from a 15N pulse-chasing experiment

“…Similarly, to its competitors, knotweed increased the nitrogen concentration in aboveground biomass where more nutrients were available, but it did so to a lesser extent. This finding corroborates evidence from several previous studies that found invaders to possess superior resource-use efficiency (Funk and Vitousek 2007;Shen et al 2011;Osone et al 2014;Ens et al 2015;Qing et al 2015). The ability to maintain a relatively higher nitrogen efficiency when more nitrogen is available-which is equivalent to producing more biomass with the same total amount of nitrogen-may be explained by a higher activity of the enzyme nitrate reductase as found by Chmura et al (2016).…”

“…In competition studies, stable isotopes allow researchers to track the partitioning of resources among different individuals or species, and thus to assess the intensity and asymmetry of competition (Kahmen et al 2006). However, so far, stable isotopes have been rarely used to study resource competition between invasive and native plants (but see Littschwager et al 2010;Werner et al 2010;Qing et al 2015;Huangfu et al 2016).…”

Plasticity of Plant N Uptake in Two Native Species in Response to Invasive Species

“…It is noteworthy that the order of N-uptake rates by four species were inconsistent with their order of total biomass. This lack of association between N-uptake rate and biomass implies that the two invasive species had higher N-use efficiency than the native species, as is common in other invasive plants [34,35]. Higher N-use efficiency rather than faster N-uptake rate appears to be a strategy that enables these invasive species to be more competitive than the natives.…”