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

Abstract

SummaryAlthough preference for NH4+, NO3− 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. NO3−, NH4NO3 and NH4+) 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 NO3− alone had better performance and greater allocation to root biomass than did plants that were supplied with NH4+ alone. Moreover, the photosynthetic rate, pigment content and photosystem II activity of plants supplied with NO3− or NH4NO3 were significantly higher than those of plants supplied with NH4+alone. The results suggested that all four invasive plants preferred NO3− rather than NH4+, and changes in NO3− played an important role in furthering the invasions of these plants than did changes in NH4+. Our results implied that decreasing NO3− may be a useful tool for controlling and managing invasive plants preferring NO3−. In addition, this study highlighted the importance of considering plant N form preference to better understand plant invasions.