## 1 Introduction  
Returning of crop residues is a common agricultural management strategy to prevent nutrient losses and to increase soil fertility. However, acceleration of N and C cycling processes often lead to increased losses of climate-relevant gases.  
Addition of plant litter to soils has been proven to increase CO\({}_{2}\) and N\({}_{2}\)O emissions over a vast range of soil conditions and litter types [1, 2, 3, 4]. Upon degradation, plant litter provides nutrients for decomposing and denitriying microorganisms. Thus, variations in N\({}_{2}\)O emissions have often been related to litter quality, especially the C:N ratio [1, 2]. For litter with C:N < 25:1, mineralization increases soil NO\({}_{3}\)\({}^{-}\) content leading to increased denitrification [5, 6], while for C:N > 25:1, N is immobilized by soil microorganisms to decompose litter C compounds [7] and restricts N\({}_{2}\)O emissions [8]. When litter quality was analyzed in more detail, easily degradable fractions explained a large share of the variability of N\({}_{2}\)O emissions [9; 10], while the lignin content was not relevant [11; 12]. Recent studies confirm that the quality of C compounds (especially water-soluble C) from litter is a main driver of denitrification after litter addition [13; 14].  
Easily degradable C compounds (e.g., sugars, proteins, amino acids, and carbohydrates) control litter decomposition dynamics in the initial phase and subsequent CO\({}_{2}\) efflux from soils [4; 15; 16]. Furthermore, the quality of organic substrates affects decomposition of soil organic matter (SOM) [17]. Readily accessible high-quality substrates increase SOM decomposition, leading to a positive priming effect in soils [18; 19]. When litter and SOM turnover are increased after litter addition, microbial O\({}_{2}\) demand increases with increasing microbial respiration. This may lead to formation of local hotspots with anoxic or microoxic conditions providing favorable conditions for denitrifying soil microorganisms [20]. Accordingly, a recent study reported the highest denitrification-derived N\({}_{2}\)O losses in soils with high SOM priming after addition of labile C substrates (glucose, vanillin) [21]. However, further studies with plant residues are necessary to better understand the interactions between C turnover and denitrification.  
The aim of this study was to investigate the effect of litter C quality and SOM turnover on denitrification. We anticipate that increased SOM turnover after litter addition promotes the formation of anoxic hotspots for denitrification and expect higher litter and SOM turnover from litter with high degradability. Thus, we hypothesize that (i) N\({}_{2}\)O fluxes from denitrification increase when C turnover from litter and SOM is high, leading to (ii) higher N\({}_{2}\)O+N\({}_{2}\) losses when litter with a high share of easily degradable C is added, while (iii) the N\({}_{2}\)O/(N\({}_{2}\)O+N\({}_{2}\)) ratio is controlled by the availability of C\({}_{\text{org}}\) in relation to NO\({}_{3}\)\({}^{-}\).  
Therefore, we setup a laboratory incubation experiment in an artificial N\({}_{2}\)-free atmosphere under fully controlled conditions. We compared different types of maize litter (fresh leaves and roots, straw) and investigated the effect of litter quality on total CO\({}_{2}\), NO, N\({}_{2}\)O, and N\({}_{2}\) emissions. To trace maize litter (C4 plant) and SOM turnover, we used a grassland soil whose organic C originates solely from C3 vegetation and partitioned the CO\({}_{2}\) efflux into its sources (i.e., litter- and SOM-derived CO\({}_{2}\)) based on the natural \({}^{13}\)C isotope abundances. In addition, we analyzed the intramolecular distribution of the naturally occurring \({}^{15}\)N and \({}^{18}\)O isotopes in the linear N\({}_{2}\)O molecule and applied the N\({}_{2}\)O isotopocule mapping approach to estimate the contribution of denitrification to N\({}_{2}\)O formation [22; 23].