**4. Discussion**

#### *4.1. Effect of Soil Type*

Our results showed that CO2-C emission from Marsch soil was higher than from Östliches Hügelland and Geest soils (Figure 1, Table 3). This may be explained by the fact that Marsch soil had more organic matter and clay content than the other soils, and CO2 emission is positively linked to soil organic carbon (SOC) content [14]. Soil organic carbon content is linearly correlated to soil respiration [20]. Thomsen et al. [21] found that the emission of CO2 from the sandiest soil was lower than from the heavier textured soils due to a low content of potentially mineralizable native SOC. Moreover, CO2-C emissions from native SOC increased with increasing clay content but this relationship was ascribed to the different mineralogy of the soils [22].

Marsch soil showed the highest N2O-N emission, followed by Östliches Hügelland soil and the lowest by Geest soil (Table 4). Organic C and clay content of the three soils also followed the same decreasing order (Table 1). Microbial community structure of a soil plays an important role in defining the rate of nitrification and denitrification in soil [23], and a soil with higher microbial activity could result in higher N2O emissions [24]. Nitrogen mineralization and N2O emissions are influenced by soil organic matter [25] and microbial population [26]. Since nitrification is primarily an autotrophic process, with heterotrophic nitrification accounting for only 20% [27], C-substrate availability and N2O emissions from denitrification and nitrification are always positively related to each other [28,29]. Abbasi et al. [30] found that the process of denitrification and production of N2O were smaller in arable soil deficient in organic carbon compared with grassland soil with plenty of organic carbon. Cébron et al. [31] reported that the presence of organic carbon promoted the population of nitrifying bacteria in a clay-textured soil. Thus, higher organic carbon content in Marsch soil could be one possible reason for higher N2O emission from this soil. Moreover, higher N2O emission from Marsch than Geest soil may also be explained by the higher pH of this soil. Fan et al. [32] reported significantly higher N2O emission rates from three alkaline soils (pH 7.6–8.2) as compared to an acidic soil with a pH of 5.6.

Nitrification is also directly influenced by soil texture [25]. A fine-textured soil can retain more water and create more frequent and longer anaerobic conditions than a coarseor medium-textured soil, and thus may result in faster denitrification and N2O emission [33]. Overall, the cumulative N2O-N emission from a clay soil was significantly higher than those from a loamy soil [33] and therefore N2O emissions increase with increasing clay content.
