Impacts of alien plant invasion on native plant communities are mediated by functional identity of resident species, not resource availability

Abstract

Alien plant invasion and nutrient enrichment as a result of anthropogenic landscape modifi cation seriously threaten native plant community diversity. It is poorly understood, however, whether these two disturbances interact with the functional identity of recipient native plants to drive community change. We performed a mesocosm experiment to examine whether the interactive eff ects of invasion by a stoloniferous turf-grass Stenotaphrum secundatum and nutrient enrichment vary across diff erent plant growth forms of an endangered coastal plant community. Communities contained 18 species (drawn without replacement from a pool of 31 species) with either runner, tufted or woody growth forms. Species were wellestablished and reproductively mature prior to S. secundatum introduction. Species growth (% cover), reproductive output, soil temperature and light availability were monitored for two growing seasons. Invasion and nutrient enrichment (two levels: ' natural control ' and ' enriched ' ) had no eff ect on species richness, community composition, reproductive output, soil temperature or light penetration. Th ere was no interactive eff ect of nutrients and invasion on community productivity (i.e. fi nal biomass), such that invasion caused a reduction in community biomass at both natural and enriched nutrient levels. Th is was driven only by reduced biomass of functionally-similar native runner species, which share similar root morphologies and nutrient-acquisition strategies with S. secundatum . Our study indicates that impacts of invasion are dependent upon the functional identity of species within recipient communities, not the availability of resources. Th is shows that management cannot buff er invader eff ects by manipulating resource availability. Revegetation strategies should target functionally-similar natives for replacement following invader control.

Nutrient enrichment alters impacts of Hydrocotyle vulgaris invasion on native plant communities

“…The decreased community evenness was because nutrient enrichment mainly increased biomass of S. viridis and had no significant effect on biomass of other species. We found no interaction effect of H. vulgaris invasion and nutrient availability on biomass of native communities, agreeing with previous findings29. However, most previous studies have shown that plant invasion reduces community biomass414243.…”

“…As such, in the high nutrient level treatment, the native species S. viridis can capture more light before interspecific competition can suppress its growth, thus developing a higher and denser canopy than H. vulgaris and shading H. vulgaris and thereby preventing its spread39. Alternatively, the spread of stolons and root development at nodes of H. vulgaris may have been limited to vacant spaces between native plants, which were diminished by the vigorous growth of the resident root systems under high nutrient conditions29. Previous studies have suggested that root phenotypic plasticity within native communities enables native plants to persist in the context of plant invasion or changing resource levels40.…”

“…For example, nitrogen addition enhanced richness and abundance of invasive annual herbs1011, promoted the spread of introduced plants into terrestrial habitats12, but increased the resistance of resident communities to the invasion by Bromus tectorum 28. Thus, different habitat-dependent pathways mediate interactions between invasion and nutrient enrichment to drive community change29.…”

Propagule pressure cannot always overcome biotic resistance: the role of density‐dependent establishment in four invasive species

“…We hypothesised that receiving communities that shared functional groups with the invader would present higher invasion resistance (grass‐only communities would more strongly resist grass invaders). Gooden and French () found that the invasion of a stoloniferous grass had the strongest impact on functionally similar native species, likely due to niche overlap, so‐called limiting similarity hypothesis (MacArthur & Levins, ). However, evidence for limiting similarity in general is equivocal (Emery, ) and may be explained by narrow interpretations of functional groups or niches, phylogenetic distance, or introduction effort (Strauss et al ., ; Diez et al ., ).…”

Functional Response (FR) and Relative Growth Rate (RGR) Do Not Show the Known Invasiveness of Lemna minuta (Kunth)

“…[15]). A competitive advantage depends on a difference in functional identity, which is hypothesised to be involved in determining the final impact of invasion [9, 16]. The competitive advantage is, in general, ascribed to the species with the highest functional trait value, while the intensity of the advantage is defined by the difference between the functional trait values.…”