The impact of atmospheric N deposition on the dynamics of various carbon fractions was investigated in two Scots pine forest soils (cambisol, podzol) of Northern Germany in microcosm experiments. Total organic carbon (TOC), CO2 emission, microbial carbon (C-mic) as well as organic hot- and coldwater extractable carbon fractions (C-hwe, C-cwe) were analyzed before, during, and after soil incubation in microcosms, run in three treatments: 0, +45, and +90 kg N ha(-1)a(-1). On both sites, the N treatment showed no response to total organic carbon (TOC) contents in most of the investigated soil layers. Microbial carbon (C-mic) was significantly increased in the organic layer of both soil types by the N application. Subsequent to the N application, the CO2 emission increased in all mineral soil layers of the cambisol but remained almost unaffected in the podzol. After the N application, a remarkable increase of hotwater extractable C (C-hwe) was detected for the organic layer of the cambisol but not for the podzol, whereas coldwater extractable C (C-cwe) concentrations decreased at both sites. The N application did not have a significant impact on the leachate concentrations of total organic carbon (TOC), dissolved organic carbon (DOC), and particulate organic carbon (POC) in the podzol, whereas the concentrations of these C fractions were decreased in the organic layer and the 35-70 cm mineral soil layer of the cambisol. The N treatment changed the contents of most of the investigated C fractions in both soil types and resulted in a considerable C mobilization. But the processes of the C mobilization between the cambisol and the podzol were completely different. According to the presented data, the cambisol obtaining moderate atmospheric N loads is much more sensitive to additional N inputs than the podzol that already received high amounts of atmospheric N.
