## 4 Discussion
### Effect of Maize Litter Quality on CO\({}_{2}\) Emissions and Priming Effect  
After onset of incubation, both litter and SOM-derived CO\({}_{2}\) fluxes strongly increased in litter treatments, while CO\({}_{2}\) efflux in Control was stable. Total cumulative CO\({}_{2}\) emissions increased with increasing input of total and water-soluble C, indicating that decomposition dynamics were controlled by the amount and quality of added plant material. The chemical composition of plant litter is known to be a primary controller of decomposition rates of both roots [11, 12, 15] and aboveground plant litter [4, 10]. Especially during the first week after litter addition, SOM turnover was increased in all litter treatments, leading to a positive priming effect. The highest increase in SOM turnover was observed after addition of maize leaves which were characterized by high amounts of easily degradable compounds as indicated by high shares of carboxyl C (i.e., organic acids, amino acids) and alkyl C (i.e., fatty acids, amino acids, paraffines) [45]. Litter and SOM-derived CO\({}_{2}\) fluxes followed the same pattern and were highly positively correlated confirming that litter and SOM turnover are interrelated. Thus, our results are in accordance with the concept that litter with high degradability increases SOM turnover leading to a positive priming effect [17, 18, 19]. Effect of Litter Quality and N Mineralization on N Emissions and Production Pathways under Oxic Atmosphere  
Directly after onset of oxic incubation, NO fluxes were highest in Control and Root while N\({}_{2}\)O fluxes were higher in litter amended treatments than in Control. The ratio of NO/N\({}_{2}\)O can be used as an indicator whether NO is produced from nitrification or denitrification [46, 47]. While the NO/N\({}_{2}\)O emission ratio of bacterial denitrification is mostly around 0.01, the emission ratios of NO/N\({}_{2}\)O from nitrification are often higher than 1 [47]. In our study, the emission ratio of NO/N\({}_{2}\)O was highest during the first 10 days after onset of incubation, with maximum values of 0.47 in Control indicating a high contribution of nitrification to NO formation. Analysis of soil samples taken prior to the onset of incubation revealed high NH\({}_{4}\)\({}^{+}\) content of soil, which further supports that nitrification contributed to NO emissions during the initial incubation phase. In Straw, where N was immobilized to decompose C compounds, NO fluxes decreased faster and were lower than in all other treatments. Furthermore, oxic cumulative NO emissions strongly decreased with increasing litter C:N ratio (adj. R\({}^{2}\) = 0.86, \(p\) < 0.001) and increased with increasing N mineralization (adj. R\({}^{2}\) = 0.57, \(p\) < 0.001) confirming that litter quality affected nitrification-derived NO emissions in the beginning of the oxic incubation phase. Addition of maize litter increased N\({}_{2}\)O fluxes compared to non-amended Control. As first, the headspace atmosphere had to be replaced by the mixture of He/O\({}_{2}\), measurements started approximately one day after onset of incubation conditions. At this time, decreasing N\({}_{2}\)O fluxes indicated that N\({}_{2}\)O fluxes had peaked within 24 h after water and NO\({}_{3}\)\({}^{-}\) addition. After this initial increase, N\({}_{2}\)O fluxes decreased rapidly and then stayed on a similar level throughout the oxic phase. Immediately after onset of the incubation, bacterial denitrification (i.e., heterotrophic bacterial denitrification and nitrifier denitrification) was the dominant N\({}_{2}\)O emitting process in litter-amended treatments as indicated by the fraction of bacterial denitrification (fbD) > 0.6. Gradually decreasing fbD values then indicate a shift towards nitrification or fungal denitrification. Litter addition [27; 48] and soil moisture of 70% WFPS may have promoted fungi, which often contribute to denitrification under weakly anoxic conditions [49; 50].