Relevance of organic vs. inorganic nitrogen in intra- and interspecific competition of seven central European tree species

Key message: When competing for nitrogen with other tree species, organic N is more important than inorganic N for most species. // Abstract: Competition for nitrogen (N) in the rhizosphere is a key process regulating a seedling´s chances for growth and survival. However, only few studies have investigated this at the individual species´ level when using a community approach. In this study, ¹⁵N incubation experiments were conducted to quantify inorganic (i.e. ammonium and nitrate) and organic (i.e. glutamine-N and arginine-N) net N-uptake capacity of seven temperate woody species co-occurring on calcareous substrate and to investigate the consequences of intra- vs. interspecific competition in a woody seedling community. The results showed that short-term net inorganic and organic N uptake capacity was unrelated to a seedling´s fast or slow growth. Furthermore, competition with other tree species did not change a seedlings´ overall capacity to take up inorganic and organic N sources. Organic N was preferred over inorganic N for most species and the preferences for specific N source shifted with competition regime and tree species. Overall, this study indicates the importance of organic N sources for N uptake in woody seedlings.