Widely naturalized species are not more promiscuous to different nitrogen forms, but benefit more from inorganic nitrogen

Abstract

Nitrogen (N) has been considered a crucial factor influencing plant invasions. Many studies have assessed responses of alien plants to different N availabilities. However, in natural soils, N comes in different inorganic and organic forms. Few studies have explored yet whether responses of alien species to different N forms are related to their naturalization success globally. We selected 22 common herbaceous species native to Germany that have all become naturalized elsewhere in the world, but vary in their naturalization extent. We grew the species under six N conditions that differed in the availability or form of N, and assessed their growth performance. We found that neither biomass production nor promiscuity to different N forms was related to naturalization success of the species. However, the biomass response to inorganic N, relative to organic N, was stronger for the widely naturalized species than for the less widely naturalized ones. Our comparative multi-species source-area study shows that although the widely naturalized species were not more promiscuous than the less widely naturalized species, they took more advantage of the inorganic-N forms. This indicates that naturalization success might be partly driven by a species’ ability to take advantage of increased inorganic N levels.