Simulating Impacts of Increased Nitrogen Deposition on the Content of Active Organic Carbon in Forest Soils Along the Urban-Rural Gradient

Abstract

Forests inside and around urban areas are subjected to high atmospheric nitrogen (N) deposition. However, the impact of increased N deposition on active organic carbon in soils in these forests remains poorly understood. In this study, we analyzed the response of the active component in the soil carbon (C) pool, including dissolved organic carbon (DOC) and microbial biomass carbon (MBC), to increased N deposition in forests along an urban-rural gradient. Experiment plots in urban, suburban, and rural forests have been subjected to three levels of N deposition rates: 0 kg N·ha −1 ·yr −1 , 30 kg N·ha −1 ·yr −1 , and 60 kg N·ha −1 ·yr −1 . The responses of DOC and MBC to added N and the affecting factors were compared among different forest types. The results showed that the concentrations of soil DOC and MBC followed a pattern of urban > rural > suburban. The increased N availability caused varied responses of active organic carbon in soils of the three forest types through different mechanisms. The decrease of DOC under N applications in urban forest soils was mainly due to the increase of DOC consumption by soil microorganisms, while the decrease of DOC in suburban forest soils was more likely due to the inhibition of microbial activity and metabolism. Continuous N applications promoted DOC and MBC accumulation in rural forest soils, which could be attributed to enhanced C and N nutrient supply capacity. Our findings contribute to a better understanding of the impact of increased N deposition on soil active organic carbon in forest soils affected by urban environments.

Keywords: Nitrogen deposition, soil active organic carbon, urban-rural gradient, Environmental factors