# Carbon and Nitrogen Pools and Fluxes in Adjacent Mature Norway Spruce and European Beech Forests
## 4 Discussion
### Tree Species Effects on N Cycling  
In the spruce throughfall, higher DON and lower NH\({}_{4}\) fluxes were measured compared to beech throughfall. Our results are in line with the study of [PERSON] and others [64], showing the importance of the Norway spruce canopy in chemical N transformation of precipitation. On average, beech stemflow accounted for roughly 10% of total N input to the forest floor by precipitation. Despite similar current N throughfall fluxes, estimated historical N deposition to the spruce forest was higher compared with the beech stand [32], suggesting higher cumulative N deposition flux in the spruce plantation compared to the beech forest. Litterfall N flux was higher in the beech stand compared to the spruce stand; however, a lower C/N litterfall ratio was measured in the spruce litter (42) compared to beech litter (52). Combined precipitation and litterfall fluxes yielded higher N flux in the forest floor in the beech stand compared to the spruce stand. Dissolved losses of N from the forest floor accounted for 16% of annual N litterfall in both stands. Forest floor N losses were dominated by DON, with higher inorganic N leaching (mainly as NO\({}_{3}\)\({}^{-}\)) in the beech stand compared to the spruce stand. Nevertheless, long-term measurements at the spruce stand revealed cessation of NO\({}_{3}\)\({}^{-}\) leaching following reduction of acid deposition [33]. Currently, N seepage losses in the 30 cm soil depth account for ca. 10% and 23% of precipitation inputs in the spruce and beech forests, respectively.  
Annual forest requirements to build up canopy foliage accounted for 45 kg\(\cdot\)ha\({}^{-1}\cdot\)year\({}^{-1}\) of N in the spruce stand and for 116 kg\(\cdot\)ha\({}^{-1}\cdot\)year\({}^{-1}\) of N in the beech stand. Those values are, with respect to the beech stand, much higher than annual N recycling through aboveground litter production and precipitation deposition. Thus, retranslocation of N from senescing foliage is probably crucial for N retention in the beech stand. We may hypothesise that retranslocation of N before the onset of litterfall prevents the ecosystem from leaching higher amounts of this limiting nutrient, as enhanced SOM mineralization and nitrification in the period of low plant N demand can attribute to the mineral N losses from the ecosystem. Calculated N\({}_{\text{uptake}}\) from soil was, due to N translocation, similar in both forest stands. Moreover, calculated potential N soil requirements were higher compared to N inputs via throughfall and litterfall in the spruce stand and comparable in the beech stand. This suggests more tightly constrained N cycling in the spruce stand compared to the beech stand. Higher susceptibility of the beech stand to inorganic N soil leaching could be due to this less constrained N cycling. However, high gross N mineralization and nitrification rates in old growth forests [65; 66] can lead to N losses when availability of labile C declines. Thus, N leaching in an old growth beech stand can be a result of C limitation coupled with a higher N availability due to the higher total N return in litter [50].