## 2 Materials and Methods
### Automated Laboratory Incubation Experiment and Gas Analysis  
The incubation experiment was carried out under fully controlled conditions using an automated soil incubation system with artificial atmosphere similar to systems described earlier [25; 26; 27; 28]. For the incubation experiment, soil moisture was adjusted to 70% water-filled pore space (WFPS, equivalent to 67.7% WHC or 31.9% gravimetric water content) and 50 mg N kg\({}^{-1}\) was added by spraying a KNO\({}_{3}\) solution onto the soil and thoroughly stirring it with a spoon. For treatments with litter, litter was homogenously mixed with soil (Maize leaves: 40.5 g FM kg\({}^{-1}\), maize roots: 42 g FM kg\({}^{-1}\), maize straw: 12.8 g FM kg\({}^{-1}\)). The soil for each pot was prepared separately to ensure the same amount of litter was added. Then, the equivalent of 2.5 kg dry soil was filled into acrylic glass pots (inner diameter 172 mm, height 210 mm) with a porous ceramic plate at the bottom and compacted in a stepwise mode by filling a 2 cm-layer of soil in pots and compacting it with a plunger. To ensure continuity between soil layers, the surface of the compacted layer was gently scratched before adding the next soil layer. Soil height in the pots was 10 cm, and bulk density was 1.1 g cm\({}^{-3}\). Each litter treatment was replicated five times, a control treatment without litter was replicated four times, and one empty pot was included as reference to determine background gas concentrations. Pots were tightly closed with transparent acrylic glass lids with rubber seals, and the outside of the pots was covered with dark plastic sheets to prevent algae growth. Pots were alternately evacuated using a rotary vacuum pump (Pfeiffer Vacuum GmbH, Asslar, Germany) and flushed with a gas mixture (80% He, 20% O\({}_{2}\)) for 24 h. The gas mixture was prepared by using stainless steel capillaries of different length and inner diameter. For the first cycles, pots were evacuated from the top and the bottom and, subsequently, flushed with the He/O\({}_{2}\) gas mixture. Then, pots were evacuated from the bottom and simultaneously flushed from the top to replace the atmosphere inside the soil column. For measurements, the outlet of all pots was connected to flow-through multi-position valves (16 ports, Vici Valco Instruments, Houston, TX, USA) with multi-position actuator control modules (Vici Valco Instruments, Houston, TX, USA), and controlled by Trilution Software (Gilson Inc., Middleton, WI, USA) via an interface module (506C System Interface, Gilson Inc., Middleton, WI, USA). The selected stream outlet tube of the multi-position valve was connected to a gas chromatograph (GC-450, Bruker, Billerica, USA) equipped with a thermal conductivity detector (TCD) for measurement of CO\({}_{2}\) and a pulsed discharge detector (PDD, Vici AG International, Schenkon, Switzerland) for N\({}_{2}\)O and N\({}_{2}\). The sample gas outlet of the GC was connected to a flow-through massflowmeter (Alicat Scientific, Tucson, AZ, USA), and a trace-level gas analyzer (CLD 88 Yb, Eco Physics AG, Durnten, Switzerland) equipped with a chemoluminescence detector (CLD) to analyze NO concentrations. To add up to the required 300-mL-flow of the NO analyzer, samples were diluted with synthetic air. Processing of GC data was done using CompassCDS software (SCION Instruments, Livingston, UK). Data from the NO analyzer and flowmeter were read out every 10 s via a serial port. The analytical precision of the GC was determined by repeated measurements of standard gases (CO\({}_{2}\), N\({}_{2}\)O, N\({}_{2}\)) and was consistently \(<\) 2%. Detection limits were 0.08 ug N\({}_{2}\)O-N kg\({}^{-1}\) h\({}^{-1}\) and 5.5 ug N\({}_{2}\)-N kg\({}^{-1}\) h\({}^{-1}\). The non-selected outlet streams of the multi-position valves were used to sample headspace gas for analysis of isotopic compositions (\(\delta\)\({}^{13}\)C of CO\({}_{2}\), isotopocules of N\({}_{2}\)O).