Stronger ability to absorb nitrate and associated transporters in the invasive plant Xanthium strumarium compared with its native congener.
Nitrogen (N) is the limiting factor for plant growth in natural ecosystems, and increasing soil N availability often promotes exotic plant invasions. However, few studies have considered the effects of N forms. In this study, we tested the hypothesis that Xanthium strumarium, a noxious invader in disturbed habitats (generally with nitrate as dominant soil N form), may have higher N uptake rates and therefore higher biomass production under nitrate treatments than its co-occurring native congener X. sibiricum. We also determined the nitrate transporters associated with the stronger nitrate uptake ability of the invader. We first compared N uptake rates and biomass production between and within these species under different N forms and levels, and then conducted the PacBio and HiSeq sequencings. Consistent with our hypothesis, the invader had significantly stronger nitrate uptake ability than its native congener and its own ammonium uptake ability. Similar patterns were also found for total biomass. Six of the seven highly expressed common NPF transcripts, especially XstNPF6.2a, XstNPF6.1b and XstNPF3.1a, and three highly expressed common NRT2 transcripts (XstNRT2.9c, XstNRT2.8c and XstNRT2.9d) may all contribute to the stronger nitrate uptake ability of the invader. The highly expressed unique transporters such as XstNPF6.2b, XstNPF6.1a, XstNPF6.2c, XstNPF6.2d, XstNPF5.2, XstNPF7.2, XstNRT2.5a, XstNRT2.4 and others may also contribute to the stronger nitrate uptake ability of the invader. Our results explain the mechanisms of interspecific differences in phenotypic plasticity and hence exotic plant invasions at a molecular level, and indicate that invasiveness of X. strumarium may be aggravated in the future under the background of global change.