Nitrogen acquisition strategy and its effects on invasiveness of a subtropical invasive plant

INTRODUCTION: Preference and plasticity in nitrogen (N) form uptake are the main strategies with which plants absorb soil N. However, little effort has been made to explore effects of N form acquisition strategies, especially the plasticity, on invasiveness of exotic plants, although many studies have determined the effects of N levels (e.g. N deposition). METHODS: To address this problem, we studied the differences in N form acquisition strategies between the invasive plant Solidago canadensis and its co-occurring native plant Artemisia lavandulaefolia, effects of soil N environments, and the relationship between N form acquisition strategy of S. canadensis and its invasiveness using a (15)N-labeling technique in three habitats at four field sites. RESULTS: Total biomass, root biomass, and the uptakes of soil dissolved inorganic N (DIN) per quadrat were higher for the invasive relative to the native species in all three habitats. The invader always preferred dominant soil N forms: NH(4) (+) in habitats with NH(4) (+) as the dominant DIN and NO(3) (-) in habitats with NO(3) (-) as the dominant DIN, while A. lavandulaefolia consistently preferred NO(3) (-) in all habitats. Plasticity in N form uptake was higher in the invasive relative to the native species, especially in the farmland. Plant N form acquisition strategy was influenced by both DIN levels and the proportions of different N forms (NO(3) (-)/NH(4) (+)) as judged by their negative effects on the proportional contributions of NH(4) (+) to plant N (f (NH4) (+)) and the preference for NH(4) (+) (β (NH4) (+)). In addition, total biomass was positively associated with f (NH4) (+) or β (NH4) (+) for S. canadensis, while negatively for A. lavandulaefolia. Interestingly, the species may prefer to absorb NH(4) (+) when soil DIN and/or NO(3) (-)/NH(4) (+) ratio were low, and root to shoot ratio may be affected by plant nutrient status per se, rather than by soil nutrient availability. DISCUSSION: Our results indicate that the superior N form acquisition strategy of the invader contributes to its higher N uptake, and therefore to its invasiveness in different habitats, improving our understanding of invasiveness of exotic plants in diverse habitats in terms of utilization of different N forms.