## 3 Results and Discussion
#### 3.1.2 Typical Soil Gas Profiles
Since also CO\({}_{2}\) and O\({}_{2}\) concentrations of this gas sampler were closer to atmospheric concentrations, (c) is most probable. CH\({}_{4}\) concentrations of all samplers showed a persistent ranking over time as observed for CO\({}_{2}\). This persistence of the ranking over time is a clear hint that our sampling and measurements are highly reproducible and that our set-up allows detecting even small changes in the dynamics of soil gases. Time series of the seasonal N\({}_{2}\)O concentrations at a depth (Figures 4 and 5) and seasonal profiles (Figure 6) showed a high variability in the N\({}_{2}\)O profile and a large overlap of concentrations between the seasons. Averaged monthly atmospheric N\({}_{2}\)O concentrations ranged from 324 to 340 ppb (Figures 5 and 6) which is half the variability as observed within the soil profile (324 to 361 ppb). Even if an increase of N\({}_{2}\)O concentrations with depth might be apparent from Figures 5 and 6, we have to consider that the variability of N\({}_{2}\)O concentrations at each depth is larger than the profile gradient (Figure 6). The weak increase in N\({}_{2}\)O concentrations in the mineral soil indicates a weak ongoing production of N\({}_{2}\)O. Yet, the N\({}_{2}\)O gradient in the humus layer was sometimes negative and sometimes positive, and often weak and not significant. This can result from (a) insufficient precision of the measurement, (b) intrinsic variability of the soil gas profile resulting from small scale processes, or (c) absence of N\({}_{2}\)O production or consumption. Regarding (a) we conclude that the observed average N\({}_{2}\)O profiles of approx. 10 ppb can be reliably detected considering the measurement precision of N\({}_{2}\)O of approximately. 3.6 ppb (Table 1). The even larger variability of 10-20 ppb between the replication samplers at each depth indicates that the lack of statistical significance in of the overall soil N\({}_{2}\)O gradient results from (b) simultaneously occurring small scale production and consumption of N\({}_{2}\)O. Forest soils can take up atmospheric N\({}_{2}\)O [19]. This would be in agreement with the sub ambient concentrations [16; 42] which were observed in the humus layer from time to time. Measurement of N\({}_{2}\)O uptake is generally very difficult since N\({}_{2}\)O uptake rates are usually very low and often below the detection limit of regular chamber measurements [42; 111]. We also observed N\({}_{2}\)O concentrations in the humus layer above atmospheric concentrations from time to time which would indicate a net production of N\({}_{2}\)O. N\({}_{2}\)O concentrations in forest soils can reach up to several ppm [76; 112]. Especially in agricultural soils, N\({}_{2}\)O fluxes can be very high after flooding or fertilization [113]. High N\({}_{2}\)O concentrations were also observed from time to time at our other soil gas monitoring plots, especially during periods of enhanced mineralization of the humus layer (data not shown). The observed N\({}_{2}\)O concentration profiles at this plot, however, did not show strong gradients and possible emissions or consumption could not be calculated. The N\({}_{2}\)O balance of a forest or agricultural site rather depends on catching the peak events [113; 114], than spanning the potentially long time between the peak events when fluxes might be negligible. A regular schedule might thus be a drawback. Covering long time series which combine discrete measurements (soil gas) and continuous measurement (temperature, soil moisture), on the other hand, allows to stochastically estimate the probability of N\({}_{2}\)O peak emissions events and to identify the drivers. This would allow then modelling the undetected peaks using the continuous proxies.