Spatial and vertical variations in the soil organic carbon concentration and its controlling factors in boreal wetlands in the Greater Khingan Mountains, China

Abstract

Wetlands have a critical impact on the global carbon cycle. This study aims to investigate the spatial and vertical distribution of the soil organic carbon concentration (SOCc), to identify the differences of SOCc among swamps, marshes, bogs, and fens at a regional scale, and finally to examine the main environmental factors impacting SOCc at different depth intervals within different wetland types located in the Greater Khingan Mountains (GKM). A total of 218 soil samples were collected. SOCc was determined by the combustion-oxidation method. To analyze the impacts of wetland type, soil type, mean annual precipitation (MAP), mean annual temperature (MAT), evapotranspiration (ET), elevation (EL), and slope (SL) on SOCc, statistical analysis methods were executed, including ANOVA with the Duncan test, Pearson correlations analysis, and the stepwise multiple regressions analysis. The mean values of SOCc in the 0–30, 30–60, and 60–100-cm intervals were 130.4, 64.2, and 32.6 g kg−1, respectively. The wetland type played an important role in the pattern of SOCc in terms of significant differences (p < 0.05) among the different wetland types in the 0–60-cm depth. However, significant differences were not found among different soil types. In terms of the wetland type, the highest SOCc was found in bogs (p < 0.05), probably due to the higher MAP and lower MAT. The increased MAP (R2 = 0.1369, p < 0.01) and decreased MAT (R2 = 0.1225, p < 0.01) had positive associations on the wetland SOCc. ET (R2 = 0.2809, p < 0.01), MAP (R2 = 0.2025, p < 0.01), and EL (R2 = 0.0484, p < 0.05) were positively correlated with marsh SOCc. Moreover, MAP was positively correlated with the bog SOCc (R2 = 0.1296, p < 0.01). For vertical patterns, SOCc was higher in the 0–30-cm interval and decreased with depth. The impacts of environmental factors on SOCc decreased with depth for each wetland type. Models were developed to document the relations between the SOCc of marshes and fens and corresponding environmental factors. Wetland types largely differed in the soil carbon pools in the GKM of China. The relative importance of environmental factors was different for the SOCc values of various wetland types. To minimize carbon loss into the atmosphere, more protections are required for wetlands, especially in the 0–30-cm depth interval because it contains higher SOCc values and is more vulnerable and less stable than those in the deeper layers.