Nitrogen uptake capacity of European beech (Fagus sylvatica L.) only partially depends on tree age

Abstract

Abstract Key message On calcareous soil, European beech roots prefer organic nitrogen, but only arginine and not glutamine or inorganic nitrogen. Abstract Nitrogen (N) acquisition is a major factor determining the processes and mechanisms involved in tree productivity, development, and competitiveness. However, only few studies have investigated changes in N capturing with tree age. We conducted 15N incubation experiments to quantify inorganic (i.e. ammonium and nitrate) and organic (i.e. glutamine-N and arginine-N) net N acquisition capacity of beech trees of five age classes. Our results showed no general pattern, but that net N uptake capacity was rather N source-specific. Inorganic and glutamine-N uptake did not differ between age classes at all. Arginine-N uptake was highest in the youngest and oldest stands reflecting a high N demand by seedlings for root foraging and biomass production despite low internal N storage capacities and by older trees for storage and reproduction. Organic N was preferred over inorganic N regardless of tree age. Overall, our study shows the high significance of organic N sources for N acquisition in beech trees.