Competitive traits of the invasive grass Arundo donax are enhanced by carbon dioxide and nitrogen enrichment

Summary Increased atmospheric carbon dioxide ( CO 2 ) and soil nitrogen (N) may confer competitive advantages to invasive species over native plant species. We conducted a two‐way factorial experiment, growing the model invasive plant Arundo donax in CO 2 growth chambers to test how CO 2 and N availability interact to affect plant growth and biomass allocation. CO 2 was supplied at c . 400 mg L −1 and c . 750 mg L −1 . N was supplied as ammonium nitrate at 640, 320 and 80 mg L −1 . We hypothesised that the fertilisation effect of CO 2 enrichment would offset limitations from N deficiency. The results indicated that A. donax plants grown with enriched CO 2 and abundant N accumulated approximately 50–100% more biomass and allocated approximately 50% more biomass to rhizomes than plants grown under ambient CO 2 conditions. Neither treatment affected the leaf area per unit mass (specific leaf area; SLA ). Greater growth will likely increase A. donax's competitive potential, because increased rhizome biomass has been associated with increased stress tolerance and post‐disturbance resprouting capacity. The consistent SLA under all treatments suggests that A. donax has a morphological strategy that prioritises increasing leaf quantity over increasing individual leaves' photosynthetic potential. These results reveal the ecological strategies that contribute to the successful establishment, dominance and persistence of this invasive plant species.