Abstract:

Soil inorganic nitrogen (N) has long been recognized to play an important role in plant invasions. Whilst comparing the N use strategies of multiple invasive versus native plant congeners along an entire N gradient is key to understanding plant invasion success, there are few related studies.

We conducted a potted experiment with six invasive and native congeneric pairs, which were subjected to 11 nitrate/ammonium (NO₃−/NH₄+) ratios (i.e. 100% NO₃− at one end and 100% NH₄+ at the other end), each with low- and high-N levels. Each species–N combination was replicated eight times, and thus there were 2112 pots in total. We measured the following traits: the total biomass, growth advantage, biomass allocation, leaf chlorophyll content and low-N tolerance.

Invasive and native congeners grew well at any NO₃−/NH₄+ ratios, and their responses of growth, allocation and tolerance were approximately parallel along the 11 NO₃−/NH₄+ ratios across two N levels. Plant invaders grew larger and had greater chlorophyll contents, higher root biomass allocation and stronger low-N tolerance than their congeneric natives. These findings suggest that invasive and native plant congeners may utilize similar inorganic N forms (i.e. NO₃− and NH₄+) across an entire N composition gradient and that higher N use efficiencies could favor alien plants to invade new plant communities where congeneric natives are dominants.

Key words: biomass allocation, chlorophyll content, low-N tolerance, N use efficiency, plant invasiveness