Considering the preferences for nitrogen forms by invasive plants: a case study from a hydroponic culture experiment

Summary Although preference for NH 4 + , NO 3 − or a combination of the two often differs among species, we know little about the responses of invasive plants to different inorganic N forms. Furthermore, many studies have suggested that an increase in N availability may facilitate further invasions. However, most of these studies predicted the positive feedback without considering the preference for N forms of invasive plants. Therefore, we cultivated four common invasive species ( Mikania micrantha , Ipomoea cairica , Wedelia trilobata and Bidens pilosa ) in South China with hydroponic media containing different forms of N (i.e. NO 3 − , NH 4 NO 3 and NH 4 + ) at equimolar concentrations. Our results showed that the N forms significantly affected the growth, biomass allocation and physiological traits of the plants. All four invasive plants supplied with NO 3 − alone had better performance and greater allocation to root biomass than did plants that were supplied with NH 4 + alone. Moreover, the photosynthetic rate, pigment content and photosystem II activity of plants supplied with NO 3 − or NH 4 NO 3 were significantly higher than those of plants supplied with NH 4 + alone. The results suggested that all four invasive plants preferred NO 3 − rather than NH 4 + , and changes in NO 3 − played an important role in furthering the invasions of these plants than did changes in NH 4 + . Our results implied that decreasing NO 3 − may be a useful tool for controlling and managing invasive plants preferring NO 3 − . In addition, this study highlighted the importance of considering plant N form preference to better understand plant invasions.